Bizzare computer crashes

Scythe

So recently my computer has been suffering from a weird problem. At seemingly random times, after at least half an hour, at most three hours, after rebooting the computer starts to lock up. Everything doesn't lock up at once. Usually it starts with firefox, though I've had the same problem with chrome. The window goes "Not responding" but I can still move the mouse. The cursor changes when it passes over buttons and edges of windows. For a short period of time I am able to click on windows other than the first to go "Not responding" and give that window focus. Once I was able to select mIRC and type "This is bizzare" before mIRC locked up too. Music continues to play, but youtube videos stop. The only thing that stops the mouse cursor moving is a CTRL-ALT-DEL, at which point all my monitors go black and I get the circular win7 doing-something cursor, forever.

It doesn't seem to be related to system load, since it locks up sitting there overnight as often as it does in normal use.

The machine reboots itself in time, and when it boots back up sometimes it can't find my system drive, an SSD, and I have to reboot it again. Other times it reboots just fine.

The only recent hardware changes I've made was adding an extra four USB ports with a dumb breakout board attaching to USB2.0 header pins on my motherboard. I've since removed it, to no avail.

What I've tried:
Verify system files, all AOK.
Chkdsk on system drive during boot, AOK.
Logged CPU temperatures until crash, AOK.
Update video card drivers, still crashes.
Unplugging all USB devices bar keyboard and mouse, still crashes.

What I'm about to try:
Keep task manager open and look for resource-hogging during crash.
Memtest86 on boot.

OS: Windows 7 64b.
CPU: i5-2500K, running at 4.2GHz
Video card: HD6900.
RAM: 8GB
SSD: Crucial M4

Any ideas?

--Scythe--

Drfuzzy

Run PC check and see what it comes up with, should be on the HiRens boot cd.

Scythe

<!--quoteo--><div class='quotetop'>QUOTE </div><div class='quotemain'><!--quotec-->Correct a condition where an incorrect response to a SMART
counter will cause the m4 drive to become unresponsive after
5184 hours of Power-on time. The drive will recover after a
power cycle, however, this failure will repeat once per hour
after reaching this point. The condition will allow the end
user to successfully update firmware, and poses no risk to
user or system data stored on the drive.<!--QuoteEnd--></div><!--QuoteEEnd-->

5184 hours, 7.2 months, I bought this computer in late november 2011. SSD firmware patch applied and it's been stable since. Looks pretty cut and dry.

--Scythe--

lolfighter

Move memtest up to first priority, I say. If it doesn't find anything, try running it immediately after the next time this happens. I'll tell you why if you need to know.

Monkfish

He just posted that he fixed it you plum.

lolfighter

Well fine then!