My computer switches on and off when in use?

It's probably an overheat problem.
With the computer on, put your hand in front of the exaust fan of your power supply. Do you feel the air blowing? Is it very warm/hot?

If you don't feel anything, that mean that your power supply fan don't work, causing it to everheat, causint it to shut down to prevent damage.

YOU NEED TO REPLACE THE POWER SUPPLY.
Chose one with the same power rating as your actual one. You don't realy need more than that.

There is at least some flow.
Your computer is probably to dusty.

Completely disconnect the power: Unplug the power line.
Take a screwdriver and remove the left side pannel.
Using a can of compressed air, blow away any dust accumulation. Put the can's nozzle between the blades of the CPU fan and blast some air there to remove any dirt cloging the CPU's radiator.

Put back the side pannel and reconnect.

Électro
August 2010