Vista Ultimate 64-bit lock up

[ThePointedHat]

I've read many threads on this topic recently, and none of them seem to match exactly what I've been experiencing. I have a custom rig with the following specs:

Vista Ultimate SP2 64-bit
ASUS M4N82 Deluxe mobo with AM3 and AM2 support
750w power supply
AMD Phenom II X4 995 Processor, 3.20 GHz
5 GB Ram (2x 2GB and 2x 512MB)
NVidia GeForce 9600 GT graphics card
Western Digital internal 500GB hard drive
Western Digital internal 80GB hard drive
Western Digital external 120GB hard drive


My problem:

Vista randomly locks up while I'm using the system. There are times when everything but the mouse will freeze, when I'm able to move the mouse around but can't click anything, minimize windows, etc.

There are times when the whole system will lock up, so that I can't use the mouse at all.

I have received the BSoD twice, and both times the computer shut down before I could read the error message.

Once, the system shut down without warning.

I have tried running in safe mode, without changes. Tried changing the voltage on my RAM to the optimum setting - 1.8 - without result. Tried switching out the power supply, updating drivers, turning off power management and disconnecting the external hard drive.

The glitch has happened while chatting on IM, while gaming, while typing in Word and while browsing the internet. It has also happened while the system idles, when it comes back from sleep mode and occasionally when I'm waiting for everything to start up after a reboot.

We're going to attempt to remove two of the sticks of RAM tonight, leaving only the 2x 2GB sticks in the system to see if that makes a difference.

Any other suggestions?