After I have been on the computer for a little bit ,it will shut off and start making a real weird noise until I unplug it. Do you know why its doing this?

It might be do to heat. Try opening the tower and vac out the dust or buy canned air and blast it out.

It sounds like you have a system problem, not a virus. The usual causes for random shutdowns are:
>Overheating triggers auto-shutdown to protect the CPU;
>Memory module going bad;
>Power supply going bad.