Q: OS X Mountain Lion only boots in safe mode!

Hey!

Of all the things you tried you didn't try these things:

go to the recovery partition by hold CMD+R while booting.

Once there, go to the Disk Utility area and Verify and repair your disks and permissions

after doing that with successful results, go and reinstall Mountain lion.

This may or may not fix your issue.

if you don't want to do that just yet, you can see if it is an application that you have downloaded that may be the issue. simply go to system preferences and choose Users and Groups and create a new user.

Log in to the new user and see if your issue persists.

When is save mode go to system preferences Users and Groups and go to the Login items and uncheck all of them.

These are the steps I would have taken first. Try these ones and see if you don't fix your issue. If you figure out what app is making you constantly restart, please let us know what it is so others may be able to solve the issue faster.

even installing and uninstalling an application will sometimes leave residual files.

follow these steps to perform what is known as a clean install.

http://eggfreckles.net/notes/installing-mountain-lion-clean/

This will delete any of your user information and start you back from 0.

I hope you have a back up?

If this is not something that is an option, I would make an appointment with your local apple specialist...

Instead of deleting your whole drive you could attempt to install ML on a partition of your drive. And then option boot into that partition.

What we are doing now is making sure your hard drive isn't failing and it is infact just something on the system....

Since you can get into safe mode, I would back up all your important files and try to start a new though. A clean install (and I rarely suggest that).

That sound is supposed to mean your hard drive is dying, I would back everything up with time machine onto an external hardrive with firewire or TB if you got it. 

I would do this immediately if you haven't already.

and then I would validate that back up by holding down option and clicking on the time machine icon in the top toolbar near the clock. doing this will give you the option to validate your back up.

Do it. and then try once more to reinstall ML from the recovery partition.

But again, hardware beeps are NO GOOD, and usually mean hardware failing. I would most certainly make an appointment with an apple specialist/genius to pinpoint what is going on.

It might be your RAM trying to be recognized. either way, a hardware beep noise instead of one that comes from the speakers, has something to do with your hardware.

Try reinstalling your ML and cross your fingers.

You should really consider getting something to backup your drive. HDD storage devices are not very expensive these days, my friend bought a 500gb external hdd for roughly 70 dollars. That would be more then enough to backup your device for a good while.

Unless of course, nothing on your computer is precious to you and you know you could easily retreive whatever you had lost before.