Computer (seemingly) randomly locking up

So I built a computer from scratch about a month ago, but I've been having some problems with it randomly locking up. First, the specs:

Intel Core i5-2500k
8gb RAM (G-skill ripjaws)
PowerColor Radeon 6850, running HDMI audio/video out to a TV set
Running the OS from an OCZ Vertex 2 SSD, have a 1tb drive for data
Asus P8P67 motherboard

Running Windows 7 Pro 64 bit, SP1

The issue:

My computer will randomly completely lock up, looping a few milliseconds of whatever sound was playing over and over again very loudly so it almost sounds like static. The entire system locks up, whatever was happening beforehand freezes and I cannot use my keyboard or mouse. The only thing I can do is hard-reboot and just wait for the next crash. I've checked event logs and can't seem to find anything, but I guess that doesn't necessarily mean it's not in there.

I had this up and running perfectly fine for a few days after building, but I'm guessing that I was just lucky and didn't experience the crashing. I've checked my RAM using memtest 86, and both sticks check out fine on all tests. I've completely removed all ATI drivers from my computer and then re-installed with no luck. I've also checked in my BIOS directly after crashes, neither the CPU or video card seem to be outside of normal operating temperatures.

The crashes occur while using Windows normally...I'm typically just running firefox, itunes, skype, and utorrent. It also used to crash after 10~15 minutes of watching video, but after I switched the video card to the other PCI slot it no longer crashes during movies, only the random lockups happen now.

I have a replacement video card in the mail right now to see if that's the issue, but could this possibly be a bad motherboard? Any help or insight would be greatly appreciated! Let me know if there's any other information I can provide.
 
Moving your video card to another slot and seeing an improvement may indicate a problem on the mobo but it might just have been a poor connection, try it again in the original slot and see if the problem returns, if it does I would say the mobo is at fault.

Having seen several instances of problems with SSD drives I would also install your OS on the standard drive with the SSD removed and see if that cures the freezing. This will indicate that the SSD is faulty. If it makes no difference then at least that will have eliminated the SSD from the possible causes.

Memtest can miss minor faults so you could also try running the PC on one RAM stick at a time to see if any particular stick or RAM slot causes problems to occur.
 
Back