Can't figure out lockup

[Politburo]

Spec: 1.1 TBird, ECS K7VZA, WD 10GB, NEC 7500 CD-R, Panasonic 8582 DVD, 256MB SDRAM (Not generic), Intel etherexpress 10/100, Innovision Tornado 3d (GeF 2 mx 400, 64MB), s3 virge (dont know manuf.), 300W power.

Made the box in September or so.. experienced lockups after coming back from 100% CPU use and cpu temp> 120 or so. In Oct/Nov, got some arctic silver and re sink-ed it, and put in 300W PS (was 250) which kept peak temps ~120-125 and seemed to stop the lockup. It now occurs again, since I moved back to school 3 weeks ago. Can be prevented by putting a floor fan on the box when running at 100%, which keeps temps to ~110. Lockup is easy to recreate by running dnet.c for about 5 minutes.. then just closing it. Sometimes system will emit high pitched beep, sometimes one monitor will go off, sometimes it just locks up (HD light solid in all cases). I added the s3 in november and it hasn't seemed to change anything. It seems temperature related (obviously), but i cant quite figure out what it is about going from 100 - 0 CPU at heat that freezes it, or how to fix it without using a floor fan.

Any ideas?

 

[DaiShan]

try a better heatsink and fan? how many case fans do you have? (add some?) I think that beep is heat related, I used to get it on my old computer after the psu fan died. is the fan on the psu spinning?

 

[bendixG15]

i second the motion....
check and fix heatsink and fan on mobo...and in and out case fans.
make sure cpu heatsink is making good contact.

 

[Politburo]

So i put in an 80mm intake at the bottom front of the case, and a 90mm exhaust blowhole right over the cpu hsf. When i first did it (at home) a had 100% load of <110F. Here at school (where i have a higher ambient, and the box is only about a foot from the cooling coils of my fridge) its ~120 after about 3 minutes of 100%. The same problem still occurs where coming down from 100% cpu locks the system. The PSU fan is spinning. The fan bearing on the GeF2 is going, but has been since about November and I had periods of no problems even with it. Also resink'd the cpu with Arctic Silver 3. I can't seem to find any cause for the problem at all.

 

[Politburo]

Now it seems to work fine again.. i just don't get it