I wonder if there is a compatibility issue between the 250GTS and some other piece of hardware you have running in that system. It's possible but it seems unlikely since the system ran fibe for over 2yrs, only change was more ram, but the issues started before that. TBO troubleshooting problems like this can be a long drawn out process unless you luckily stumble on the answer (as your already finding out),
Just so we can rule them out have you ran a chkdsk and tested your RAM? In cases like this you just never know and i've seen HDD problems though up all sorts of issues. Test your RAM with memtest:
Memtest86+ - Advanced Memory Diagnostic Tool
Memtest turns up clean (also used my old ram to check but also clean and still freezes), chkdsk performed, HDD diags, WD lifeguard,and so on..all clean..Only after a couple of freezes my ntfs gets a bit jumbled but thats more a symptom than a cause, because after one descent boot the "issues" are ok again.
When you go to run the chkdsk it will say no need to scan but run it anyway.
Lastly can you open up the run app and type 'dxdiag' without the quotes and click ok. Once opened click save all info and post in the forum (using the 250GTS of course)
Event viewer clean, first thing i checked.DXdiag ran already but not copîed (was issueless eather way) Problem is i can try and run it, but not sure if i can do it without my pc freezing while trying
. But i'll swap the cards once more.Cooling wise my pc should be ok,yesterday i did a furmark with my 250gts and there I noticed that under stress it goes up to 86° which is quite high, but the card can go up to 105 so it shouldn't be a reason for flipping.In normal gaming card is 65 or so, and idle its 45 orso.I have 3 casefans plus a big copper zalman for my cpu.If anything i would expect to see graphic issues on my screen before it falls out.But there is nothing, and no errors which makes this thing so hard to tshoot.
Check your event viewer, see if anything relates to the freezing. Also what's the cooling like on the 250gts and in your case? This might answer why it runs ok in a different machine and the 8600 runs ok too (depending on the cooling it has and if it differes from the GTS250)