I might have been having a similar issue. It might be one or both issues causing it. One you have a older pc and you have never reapplied the paste between cpu and heatsink. I have read you need to change that every 5 years or so. I got like a 15+ drop in temps after I did that on my system of 10 years. Other issue is you need to dust the air vents because the system is over heating 2nd is, video card is getting a voltage drop, or not properly seated in its pcix slot. My issue was probably the above two, but the one that was the main issue was the voltage. So I took the vid card out, dusted the slot, stuck the card back in, and rotated the power cables to the video card. So I had a 8 pin and 6 pin, and when I put them back in, I made the old 8 power to a 6, and the 6 to a 8 and plugged them back in. Since I did that, I stopped having the issue. So pending your power supply and wattage, try using diff pcix cables to the vid card or perhaps your power supply fan went out and its overheating causing a drop in power delivery. Spring