Yesterday I was working on my computer (which is fairly old) and suddenly it turned off. It has happened two times. After the first time I just held the power button for 60 seconds and it turned on. At night it happened again, this time the same method didn't work. I've read about most solutions too but none of them worked either. (removing the memory modules, replacing the cell battery, etc)

The motherboard is getting power (orange light) but it doesn't beep. When I try to power on the computer, the fans start spinning but immediately stop again.

So, which part of the computer should I replace? It worked completely fine before and it was also very fast. It was in good shape for an old computer...

Or should I just get a completely new computer?