Hi. So when you turn on the computer that was freezing, nothing happens? Do you just get a black screen? If so, have you tried to unplug the monitor while the freezing pc is turned on while the screen is black? If you unplug the monitor while it is plugged in, no matter if the screen is black or not, it should at least recognize that the monitor has been disconnected and give you a warning message. Try that. If you unplug the monitor while the freezing computer is on and you get that warning, at least you know it's probably not the video card.
Do you get any text on the freezing computer at all when you power on?
Had you recently installed any software of hardware?
Did you ever get any Blue Screens with any Stop Errors?
I would like some more specs on your computer like:
Brand
Processor
RAM
HD
Motherboard type
Has this computer froze before this?
Are you able to press F8 when you boot up to get into "Windows Advanced Options"
You can also try resetting the CMOS jumpers
Near the CMOS battery on the MOBO there are 3 PINS called jumpers.
Two of them should be covered by a piece of rubber.
If that rubber piece is on PINS 1 and 2 you would move it to PINS 2 and 3, leave it there for 5 seconds, and move it back to PINS 1 and 2.
Do it the opposite if the rubber is already covering PINS 2 and 3.
After you do that you should be able to turn on your computer and at least be able to tap F8 to get into "Windows Advanced Options" or "F1 or DEL" to get into your bios
Anyways get back with me with some specs and try those things I said