Mysterious Freezing

[Ian Gibson]

On FreeBSD 6.1, I am experiencing a problem involving my system freezing. This 
happens at irregular intervals, on the order of days rather than hours or 
weeks. It is a total freeze; everything on the screen becomes completely 
static, no response from the mouse or keyboard, Ctrl-Alt-Backspace does 
nothing, etc. Earlier, the freezes would only be partial (mouse pointer 
stuck, but OS accepts input from keyboard) but would happen every few hours. 
I tried altering IRQs in my BIOS, and now the freezing only happens every few 
days, rather than every few minutes or hours, but now when it freezes, it 
seems to be totally frozen (i.e. ctrl+alt+backspace does nothing).

Copying files from a different OS on the same HD often causes a freeze, as 
does copying files over my wireless network. When a background fsck is taking 
place (after a previous freeze and hard reset, for example), the PC will 
often freeze again. I notice all these things involve heavy HD access. Am I 
right in suspecting IRQ issues as the likely culprit? What steps shoud I take 
to resolve this?

I am using a custom built PC with a radeon 9250 graphics card and 3D 
acceleration enabled. Occasionally when running a 3D program, I get the 
following:

taxa% bzflag
Mesa: CPU vendor: AuthenticAMD
Mesa: CPU name: AMD Sempron(tm) Processor 3100+
Mesa: MMX cpu detected.
Mesa: 3DNow! cpu detected.
Mesa: SSE cpu detected.
r200WaitIrq: drmRadeonIrqWait: -35

and the program crashes after a couple of seconds. This will happen every time 
for all 3D programs. After a reboot, either the same thing will happen again, 
or all 3D programs will work fine.

Could this be related to my freeze problem?