Computer randomly BSOD/Freezing??

Is your memory set to default voltage in bios? (1.5v I think)

And take a look here http://msdn.microsoft.com/en-us/library/ms854226.aspx

Have you set the memory to 9-9-9-24?

Sounds like a driver issue, have you got the latest bios for you system and the latest GPU drivers.

http://www.reviversoft.com/blog/2013/08/apc_index_mismatch-blue-screen/

Check current bios version in bios or with cpu-z.

Downloads here - http://www.gigabyte.com/products/product-page.aspx?pid=3519#bios

I would try removing all system and gpu drivers and starting again, what drivers did you install when you loaded Windows 8?

What revision is your board? 2.0 / 2.1 / 3.0 / 3.1? and what BIOS version is currently installed?

I would definitely update that bios to the latest F6.

Also download and install all the other drivers from the Giga website now you r running W7.

I am assuming u have all your other bios settings set to auto and aren't OC ing anything.

-Since you wiped out your windows and did a reinstall you really want to make sure you install the service pack and updates
otherwise you will hit a bunch of known bugs in windows if you use a current graphics card driver.

Normally the bugchecks you are getting indicate that the content of the kernel sharded memory for device drivers is being corrupted.
there are some hardware things that can cause that (incorrect overclock, incorrect voltages to CPU memory controller, incorrect voltages to RAM chip,
incorrect RAM command channel setting on the RAM timings (2T or 2n not selected when required and the default value of 1n being used in BIOS)
Most of these errors are worked out buy getting a clean run of memtest86 on its own boot CD.

So, assuming that a memtest8t test actually passes the most common problem will be cause because a driver wiped out another drivers data
and the other driver went to use it and had problems and bugchecked. It is kind of hard to find this but window helps by loading drivers in different orders on each boot. At sometime the bad driver will attempt to mess directly with a windows driver that is checking for data intergrity and windows will bugcheck and name the offending driver. The bugcheck will indicate a buffer overflow.

Most often it is just faster to look at the memory dump and list the old 3rd party drivers as suspects for the corruption and remove or update them.
(the microsoft drivers get reported by the WER system and updated by windows update and tend not to be the cause of the issues. The detected errors in the 3rd party drivers are given to the driver manufacture and Microsoft is not allowed to install the fixes for various reasons. The result is most of these memory corruption errors are being caused by 3rd party drivers even though they are known problems with fixes that just have to be installed from the 3rd party)

The general solution for a end user is to just install as many driver updates as you can get your hands on and hope your problem goes away.
if that fails you have to use verifier.exe to turn on special checking on your computer. This checking will try put special checks around drivers databuffers and if the driver over writes its owned memory space windows will bugcheck and name the driver and you will know who caused the memory corruption. (the checking slows down the computer but catches the driver, you have to run verifier.exe /reset to turn off the checking or your computer will run slowly until you do.)