what is a good but free virus scan?

my pc used to have panda virus scanner before the technician worked on it but changed it with a new one. each time i open my pc it says "comouter might be at risk" and that the security is not activated. but when i do activate it, i ask for a package key which neither me nor the tachnician do not have. someone said there is one via net. Tried the free virus scan but all it did was scan and nothing else unless i pay but i dont have cash nor credit card.my pc is at rish, really?

I need a link for free virus scan to remove viruses

My comp keeps rebuting by its self and it keeps freezing up. I think it has a virus but I can’t scan or remove with out paying and I don’t have a credit card. I’m hoping there is a free scan and free removal tool some where on the web.

I have problems with my pc after getting into a site .
I need a good virus scan .software for my pc and internet.
any suggestions?