Completely Lost on Overheating

Okay, I thought after three video cards, I had this problem licked, but it's still happening, and I'm at a complete loss, so I'm asking for assistance.

I have a AMD 64x2 4200+ Vista system running 2GB of Ram with a 8600GT 512 card (more on the card part later). The problem with the system is that it runs great at idle speeds (Ntune reports it at 125 F idle), but when I try to take it to load, it bumps to 135F before completely crashing, or in benevolent cases, merely just shutting down my internet connection (go figure). The longest duration from start to crash has been two hours, the shortest time two minutes.

I suspected at first it was the video card issue (it still may be). My first card, a 7600, died on me but ran great, so I bumped up to an 8600 to take advantage of DX10. Immediately the problem occurred, so on the advice of several people I installed a cooling item (passive cooling on the card). This worked for about two minutes before it crashed again, this time taking the card with it. On the advice of another friend I bought another 8600 GT 512 with a copper active cooling fan built onto it; I also installed a slot fan just to be on the safe side. Well, the fun and merriment of crashes continue unabated.

This is really getting annoying, as it's affecting gameplay, but more importantly, it's affecting rendering and use of art software that I use for my job. I'm not ready to sink into watercooling just yet (the joys of being a starving artist), but with replacing the fan, slot fan, and running the card's fan at maximum via NTune but still having it crash left and right I'm at my wits' end. Any help would be much appreciated.

 

It might be time to start looking at your CPU cooling. Have you removed, cleaned and refreshed the thermal paste on your HS yet? So your CPU is at 125 then 135 and your system is crashing?

How about you try another temp monitoring software and compare the 2 and see what your CPU temp is at, also immediately after the next crash can you go into BIOS and note what temps are there please:

http://www.majorgeeks.com/download.php?det=4181

 

Have you tried running the system with the side cover off and then checking your temps. If this also leads to crashes, then with the side off get a domestic fan and direct the air flow to point at the case.

You have not stated what sort of rig you have but overall cooling to include the case and air flows is extremely important. Taking the side of the case off will in the first instance lower all the temps and will also give you an idea of how good your overall cooling is.

I am of course assuming that the stated temps refer to the cpu and if so are too high. Idle should be (depending on season) mid 30s C and load mid to high 40s C. As has been stated already your cpu may need to be re-greased and the hsf cleaner properly.