OK, I've re-tested the RAM and all the RAM slots, still nothing. HOWEVER, I've noticed that if I drop from using 8GB RAM to 2 or 4GB then the machine runs just peachy.

What's going on 'ere then? Never had any problems running 8GB before, but now with 8GB the machine locks up/BSOD or reboots randomly.

Which OS does this happen with?

It's probably a badly behaved driver. Most likely the graphics; especially if it's ATI. What graphics are you using? Is it Turbo-cache or "proper" memory? If you're using a 64 bit Windows, are all your drivers signed? Are they third party, or the ones from the Windows disk?

If it's Linux or something else, then I haven't a clue. For some reason, I always figured you're a Linux user.

It's Windows. All drivers signed and up-to-date.

The problem occurs in both Vista x64 and Windows 7 x64. No problems in Linux.

My mobo is the ASUS M3A32-MVP Deluxe Wifi edition.

My CPU is the Phenom II 955.

The memory I'm running is 8GB of this: OCZ Platinum Series 4GB (2x2GB) PC2-8500C5 1066MHz Dual Channel.

I read that some people were having issues with my combination of mobo, cpu & 8GB RAM were having trouble since the 1705 BIOS revision, so I've reverted to the previous 1604 version to see if it makes a difference.

If not, I guess I'm stuck using 4GB until further notice.

I'm probably jumping the gun in saying this, but rolling back the BIOS version from 1705 to 1604 seems to have done it.