I own a 2006 iMac, which, alas, has a known manufacturing fault. Because of the poorly-designed cooling system, the graphics card (soldered to the motherboard) has become defective and the system shuts down spontaneously minutes or seconds after being turned on.
I have used a different computer for three years and I have really no need of this iMac at the moment.
However, I'd like know if I can nevertheless do something with it. It has a processor, lots of RAM, and a good hard disk. Can I use its computational power and its hard drive without employing the graphics card? I'd like the idea of turning it into a file server and being able to run non-graphical programs in it. The best would be being able to run X11 programs in it and see their graphics on another computer.
Everytime I turn the computer on it only worsens the problem, damaging the graphic card even more. So far, it didn't shut down when I put it in "single user mode", but I am afraid that even this little workload could damage the graphics card more and more. Basically I do not want to use the graphics card at all. I am prepared even to install a different operating system. (But how would I do so when the computer keeps shutting down?)
Edit: The problem is also reported in this petiton