This could be an old laptop where the owner never heard of canned air, or they installed torrent software. The list is far too long to put here.
As to the VIRUS, why do you suspect that? Slow operation is caused by far more things than that. I would not scan for this yet but if you must, Grif has a fine list at the next link.
I turn my laptop on and put in the password for it to begin to startup. After I put in the password the computer does not load further. Therefore, my laptop does not allow me use the internet or any other programs. Once in while my computer will actually start up, allowing me to use the internet and open up other programs. Even when this happens, my laptop acts very slowly and is almost unusable . This speed is a lot slower than normal. What could be causing my laptop to be doing this? Could it be possible that there is a virus on my computer? Help me out guys.