The only way I can use the computer is in 'Safe Mode' which doesn't allow sound or video?

You may have to read up about how to find more information on how to handle startup issues, and perhaps perform disk maintenance with Disk Utility; or maybe even do some other tactics.

•Resolve startup issues and perform disk maintenance with Disk Utility and fsck:

http://support.apple.com/kb/TS1417

In Mt Lion, you may have a Recovery partion with OS X Utilities, so that is an access point to use Disk Utility and other tools. This unmounts the boot volume the computer normally runs on, so it can be repaired.

•OS X Tips - Using the Recovery HD:

http://pondini.org/OSX/RecoveryHD.html

If your OS X 10.8 is up-to-date with last update step in the series, it would be 10.8.5; so if that's not where it's at, consider after attempting to resolve the issues you face first, then update with the Final step from this page:

• OS X Mountain Lion Update v 10.8.5 (combo)

http://support.apple.com/kb/dl1676

Sometimes, reinstalling the last update (above) again can help with

some issues in a Mac OS X system. If running Disk Utility from the

recovery in Mt Lion to repair disk + repair disk permissions, does

not completely fix issues, you could download the Combo & reintall it.

And use Disk Utilty in the running system to repair disk permissions.

{after the item above, restart; + run Software Updates in your Mac}

The keyboard combination you cited for reset of NVRAM PRAM is

not a startup repair device, and has limited usefulness. You may

have meant this other thing, it uses fewer keys than the above...

The Command + R is a means of startup into recovery mode

where you can access the OS X Utilities from a special partition

in the OS X system, helpful in newer Macs that don't have an

optical drive, but do have Recovery in a partition in the HDD.

And if this does not work, some suggest trying the NVRAM reset,

as it may help fix an issue that could contribute to not accessing

the Recovery partition, if available, in an OS X 10.8.x system.

However the suggested earlier methods in the Support link to

repair disk are marginally successful, you could attempt to reinstall

the Combo 10.8.5 update. Sometimes this can fix odd things.

Unless you recently installed new software that added fonts or

odd drivers that may not be compatible with your OS X.

If you installed new fonts as part of a printer driver, or other new

applications, there may be a startup issue relating to new stuff.

The computer could start OK in safeboot, but not with the other

things loaded during a regular startup. Troubleshooting starts with

knowing what you did recently that may have contributed to the

situation at hand. Safeboot helps by allowing access to System.

A few ideas & more lengthy look at safeboot & other ideas, here:

http://computers.tutsplus.com/tutorials/5-more-quick-fixes-to-common-mac-problem s--mac-45525

There likely is a lengthy Console log file that could show some

issues based on time and day when you try to restart from Safe

Boot mode, and what does or does not load correctly may be in

those System Logs in Console utility.

Several things may be behind it. Perhaps OS X Utilities in the Recovery

partiton boot volume can help fix the hard disk drive or permissions, if

so then other things may be needed to bring the system up to standard.

Not sure if any of this may help.

Good luck & happy computing! 🙂

So when you try & run the computer without SafeBoot on a restart,

what does the display do? - Does it try to go to the desktop screen

but fail with a grey screen, or with an apple and whirling disc icon?

If there is some kind of action at that point before it 'fails' the details may be helpful in further troubleshooting the issue. However the problem sounds like something in the main user account and if you had a second user account (you could make one, give it Admin privileges & permissions, like your main one should have) that may help to attempt access to and repair the main user account.

When you started into SafeBoot, you probably had to login with your user account password or an admin password, so when restarting from SafeBoot, again after regular login failed, did you have to enter your password again? That would be the expected normal, in OS X. However that may not happen if there are errors or other conflicts in the user account you are having problems with.

It may be possible to try & make a new user account, then see if the computer can be set to start up from that account by default. If it can, it may be possible to use that new Admin level account to run the computer, and then do more research on how to move the other account stuff into the new one.

Not knowing the history of any later applications, fonts, or third-party software into your Mac, makes it hard to determine what is in your user account that is making it not want to start. Could be something introduced or installed there, maybe unknowingly as to what it may do.

You could try re-wording your issue and surmise the issue to consolidate all this, then post a new topic in the Mountain Lion 10.8 ASC discussions area; so as to attract someone with system knowledge. Maybe someone who can outline a path in easier to follow terms. Or, it may be worth taking the computer to some expert or Specialist and ask. Even an appointment with a Genius at an Apple Store may help figure out what to do next. If you call ahead before a visit to an official Store, you can set an appointment for this issue. The diagnosis and some help (for awhile anyway) may be without cost. A repair would be another matter.

http://www.apple.com/retail/geniusbar/

Could be the hard disk drive may be defective or there may have been a Firmware Password on the drive; these kinds of things are best handled by making a backup clone or copy to an external hard disk drive and then replacing the internal HDD (if testing shows it suspect) so later the backup user work files, images and maybe music files could be migrated or moved back into the computer from the external HD later. Drives wear out or defects can corrupt data, so as to affect use of the computer. It could be replaced, if so.

{If you did not need anything from the hard disk drive in your MacBook, you could ship it away for a fairly good repair inspection and have it return from a specialist in SC by the name of wegenermedia.com. I did that with one of my Apple portables when the shops here wanted 4x the cost, and they were also shipping them stateside from Alaska. They 'gave me the business' with faulty AppleCare repairs in Anchorage, so why promote them? Two of three co's are gone, failed. Before the new official Apple Store arrived.}

There are tons of stuff online about the safeboot topic and various issues, including some like yours where the computer won't run except in safeboot mode. Usually that helps because one can look through Console's utility logs on system related issues and look for odd information. These things take time, and new skills.

Because the computer in Safeboot is not running the entire OS X and its extensions, etc, the sound and other things will not work. There is something in the system (your user account) likely behind this; so if you could go into System Preferences> Accounts and look into users, you can make a new Admin account. And set a new password for it, give it Admin level, and change the account the Mac boots from, to that one. Then restart.

•There also is a way to get a file log of the system as it is, in your MacBook, by use of a free utility, and the report from that log may be helpful if posted into a new ASC discussion...

Here is a link read about, another to get it.

About Etrecheck:

http://www.etresoft.com/etrecheck_story

Etresoft: EtreCheck: download

http://www.etresoft.com/etrecheck

Some of the more technically minded volunteers in these ASC discussions are able to provide lengthy replies with complex paths, that if followed, may be helpful. And they all take time. Been awhile since I sat up for 40 hours straight time working on a Mac. I spent months trying to get an iMac figured out, it was under AppleCare so I could not open it due to the warranty. But the shop I had taken it to could never find anything wrong, so I spent 7 months of the first year driving it hundreds of miles to-from the authorized shop. They would say they were done with it, after a week at their shop, so I'd drive 200 miles to get it. Then drive home and within an hour (after it warmed up from the cold trip first, as I took along the box and plastic to seal it for the drive in winter) I could repeat the same crashes, same logs, and everything I had detailed in significant order and handed their 'expert specialist' -- and I am certain they did not try what I had done.

I'd rather have a puppy or kitty than work on these things to the level I had before, for fun. The fun went away with the two newest computers I ever had, both had Applecare extended plans and no local support. But I had fixed restored repaired & donated over 200 Macs before those two, not in a business, just at home. A fun learning experience, at least until those new ones. The failure of those stopped thoughts of advancing into more digital photography, though I have cameras, I also have collectable film models that are fun to use on rarer occasion.

A list of things in your computer may help, see etrecheck...

Good luck & happy computing! 🙂