Computer problem

3 months ago some idiot came to visit and went on my computer they were trying to download a popular game called minecraft it didn't work because my computer doesn't have any kind of video card to play games its just barely let's me watch YouTube. Anyways they had something come along with the game called winzip this program comes on and tells me to download it I didn't want it so I ignored its now it trys to down load and scanner and boom it shuts off my computer grrrrrr I can't keep my computer on even in safe mode with or without networking in normal start up it won't let me use my mouse keyboard I don't know what todo and I am not a computer repair woman so what can I do I went out and bought nortons Internet security/nortons utilities it won't let me put this program on to eliminate the problem what can be done thankyou. HELP please thanks .