after an update, my system won't boot, or start up on safe mode

Calm down a bit and carefully explain from the top, what happened, what you did, what is on what drive, what machine you have and so forth.

Sort of summerize it in a chronological order so we can develop a mental picture as we can't see anything and can only go by what you say.

Thanks 🙂

Root user is turned off by default for a reason, it leaves your entire machine open to chnages/attack.

The initial first user when you install OS X is Admin and it's sifficent for most users.

If this is a more recent iMac in the last year or two, Apple has installed something on the hard drives for heat control, only Apple can replace the hard drive now. 😟

I think you should first:

Disconnect all drives

1: c boot off the 10.6 disk and use Disk Utility to erase with zero the new internal drive, then partition format Options: GUID, format OS X Extended (j), give it a name and click apply.

2: then quit and install 10.6 on the new internal drive and reboot, then use Software Update to get to 10.6.8

3: next hook up the external drive with your files again and transfer a copy to another drive so you have more backups

In your first post you said your DVD drive is not working, well Snow Leopard can be installed via a USB key, but you will need another Mac to copy the 10.6 DVD to the USB

http://www.maciverse.com/install-os-x-snow-leopard-from-usb-flash-drive.html

Once you have that you can hold option key and boot from the USB and install it.

Apple didn't cut off holding the option key and booting a external clone.

What is on the external drive? Is it TimeMachine that was on 10.7 previously?

I don't have enough information here what you had, what your were trying to do and where is everything now?

Were you trying to revert back to 10.6?

Please more information. 🙂

Details please. thank you. 😉

Smash87 wrote:

no it was just a normal data, libraries, etc....i copied them and everything was ok

i made the update to the internal HD system😉

Well if your DVD drive doesn't work, how then did you get 10.6 onto the new internal 1TB drive?

Or how did you get 10.6 onto the external 1TB drive?

Still there are glaring lack of details, I'll have to go now as this has turned out to be fruitless.

Post your question once you have figured out what you did. 🙂

Smash87 wrote:

... still having that issue that my external HD is still locked for unknown reason...i tried disk utility but the verify or repair permissions buttons are inactive...

Permissions verify or repair are only applicable to HD volumes that have a bootable OS installed on them. (Other volumes lack the database of expected permissions settings, & even if they did it would be invalid.) Also note that it is not necessary to run the verify before running the repair -- the verify is useful only if you want to check permissions settings without changing them.

I strongly suggest that you not try doing anything from a PC that you don't have to -- this may be part of the reason you are having problems with the locked disk. It's OK to use "Remote Install Mac OS X" with a PC's optical drive to reinstall Snow Leopard if you follow Apple's instructions exactly, but don't try a permissions repair this way. Instead, run the repair after the OS is reinstalled from that copy of the OS running on the Mac.

Also, don't use single user mode unless you have to -- this is equivalent to logging in as the root user so the normal safeguards that prevent you form doing things that can damage the OS or file systems of attached disks don't apply.

If you want more useful help with this, you really need to explain everything you have done as clearly & completely as possible. For instance, we still don't know how you managed to install the OS on your replacement internal drive without a working optical drive. If you explain exactly how you did that, it might give us a clue about why you are still having problems.

One other thing: when you say the external disk is locked, do you mean that "Get Info" for it shows a lock icon in the bottom of the window, or that you can't access anything on it? If it is just the lock icon in the Get Info window, this is normal. To unlock it, you need to click on the lock icon & supply your admin user info. However, do not do this to make changes unless & until you are certain the disk's contents are not accessible through the Finder or it can't be selected as a Time Machine backup and you have posted in detail what you did to make sure this is true.