Alright, so this is roughly the problem (and pardon me for not being very clear, since my monitor won't turn on, I can't remember exactly what it said):
The computer is supposedly not very old (but who can you believe, right?), it's a Pentium IV processor with a newer monitor. It actually belongs to my grandfather and I don't work on it. Lately it started spontaneously freezing up and the restart button and/or ctl+alt+del didn't work. We had to press on the powerbar button that it's connected to to restart it.
Then, today, it started up normally but then started running in circles. It starts up, checks memory, then restarts again. The message that it displayed was something like 'CPU is not readable (or configured??), please check CPU Soft Menu' (which is in setup).
So, I checked the CPU Soft menu and since I have no idea what it all means, I tried changing the settings but as soon as I pressed 'Save&Exit', it restarted again and when I went back to the menu, it had the old values for the CPU. Then, out of the blue, it stopped turning on the monitor. The processor would make a normal sound but the monitor wouldn't light up (though it's plugged in and it's working).
At this point, I guess the only way to do it is do something physical with the processor, right? But what? I'm not going to mess with it myself. I'm computer literate but I'm not a technician. I only cleaned the fan and inside of the processor very gently but it didn't do anything.