Hey i have a real problem here!

about 3 days ago i got a virus (i think), it started to restart my computer at different times, giving me 50 seconds to finish everything i was working on, but now it lies in my taskmanager as a program called SYSTEM. it keeps sending and recieving data and it slows down my computer by over 70%... anyone else had this problem and what can i do? please help...
