Given the age, after a few years the heatsink compound can dry and crack. Did you do the work necessary to replace that and be sure the heatsinks are on proper on all things that have heatsinks?
My setup is:
MotherBoard: Asus p8H61
RAM : 2x 4GB Corsair CMV4GX3M1A1333C9
CPU : Intel Core i3-2100
GPU : NVIDEA GTS 250 / Raddeon HD 7870
PSU : Cooler Master RS-650-PCAR-E3 (650W)
Windows 7 64bit Enterprise / Windows 10 64 bit Professional
I had been utilizing my GTS 250 with 1X4 GB and Windows 7 64 bits Enterprise and had almost no problems for 4 years except for the fact that sometimes my computer would stop working and the display would freeze, I would restart the computed. Sometimes it would go back to normal and others it would beep 3 times and a text would appear 'CPU fan not working'. I would then open my computer and see that the CPU fan was stopped, but when i touch it it would start spining. Then the computer would go back to normal.
Some months ago I bought 4 GB more RAM, but the computer worked normally.Two weeks ago I bought one Raddeon HD 7870 from a friend and at first it would work normally, I did a Furmark test for 30 minutes with no problems, the temperature was stable at 80ºC and I saw no artifacts. I've played games like Skyrim and The Evil Within on max settings since then with no problems.
Two days ago I was playing skyrim when the screen turned black and there was a strange noise. Nothing would work then I had to restart the computer. It then worked fine and i kept playing.
Yesterday the same happened while playing the Evil Within, I then thought it could be a driver or Directx problem. I updated to Windows 10 and Directx 12 but the same problem happened. I then runned a FurMark test on the HD7870 and It Crashed within seconds, showing blue artifacts and with GPU temperatures of 70-80ºC. I had to restart the computer.
Then my computer Wouldn't Start, It would show the Windows logo but after a while it would show artifacts and crash.
I changed back to my GTS 250 and It worked fine.
Today i tried the Haddeon 7870 again but when i tried to turn on the computer it would make shock sounds and would only start spining the coolers for less than a seconds before it turned off. I thought then it was a PSU problem, when i tried to run the computer with the raddeon 7870 powered by only one 75W 6pin the computer turns on with all then fans working, but no display shows (obviosly cause the GPU requires 2 75W 6pin) and it makes 3 beeps.
I'm now writing this utilizing my GTS 250 and the computer is running normally, but yesterday I ran a FurMark test at this GPU and the temperatures reached more than 100ºC in seconds and I turned it off being afraid the GPU would burn out.
Is my raddeon 7870 dead or do I have a PSU problem?