I have an OptiPlex GX520 (Small Form Factor) that I mothballed a couple of years ago because it kept locking up on thermal events.  I'm trying to press it back into limited service for a particular task.

Before I "retired" it, I tried most of the obvious things -- blowing out the case (the CPU heatsink WAS dusty, but not horrible), and replacing the CPU (with fresh Arctic Silver) a couple of years ago, and it still locked up with thermal events, so I gave up for a while and threw it into storage.

Today I replaced and the CPU fan on the front of the case.  It ran a while just fine, and then locked up after 15-20 minutes of nothing special (I had a CMD prompt open, and was in the middle of changing directories).

I just re-booted, and started two simultaneous FLAC encoding sessions running 10 times back-to-back, on 700 MB files.  The (combined) CPU utilization was at 97-99% for nearly an hour -- no thermal shutdown. If I truly had a heat issue, that should have sealed the deal.  I'm beginning to wonder if I EVER had a true thermal problem -- could it be whatever is SENSING the temperature is generating false alarms?

I couldn't find the CPU temperature anywhere, but I have CPUID's HWMonitor running, and it says the hard drive temperature is holding at 47C (116 F).  A bit higher than I'd like, but certainly not meltdown range.  It's inside an air-conditioned home, at 77 degrees (give-or-take; it's hot here in the summer)

I know that packing that much into a SFF case is asking for heat problems, but it seems more and more like something else may be going on.

Any suggestions?