When I got a virus in Oct. - it did several things...
it froze the computer a lot so I had to reboot (which I discovered later FEEDS the virus),

it said I didn't have memory yet I was only running 35%, plus was defraged

and it created a registery error - which is when I sought professional help...

Free virus scan using most current protention/ dats at link below.

http://security2.norton.com/us/intro.asp?venid=sym&langid=us