CPU fans running at high speed, means the CPU is getting
warm, and is perhaps stuck in a loop. Or, if the CPU fan
is being controlled by a program like Speedfan, perhaps
the fan control program crashed. The monitor going off,
means the video driver may have played a part in the
crash of the system.
Does the PC start OK now ? Have you been able to
boot the computer ?
Check the Event Viewer. Settings:Control Panel:Administrative Tools:EventViewer.
In there, errors are recorded, and perhaps when the computer
crashed, there is an error recorded there.
Open the computer and inspect it for physical problems.
For example, sometimes a heatsink will break away from
the socket, due to some cracked plastic. Or perhaps
some capacitors are bulged. Perhaps a problem will be
evident when you have a careful look at the condition
of the inside of the computer.
Many millions of motherboards have had this problem, of
bulged capacitors. Bulged capacitors lead to unstable
CPU operation, and increased crashing. Eventually,
the computer will no longer POST. If the capacitors
are bulged like this, and you are proficient with a
soldering iron, the capacitors can be replaced. But
to have a repair man do it, will cost too much money.
It might be just as cheap, to replace the motherboard,
if you see what is shown in this picture.
http://www.badcaps.net/images/caps/kt7/image004.png
Paul