My computer always seems to be freezing up shortly after I start it, is this a virus and has anyone else had this problem?

You might want to defragment, or if you have, start your computer in safe mode, toggle on the option to see hidden files and folders, and then do some browsing in your hard drive. If you further suspect a virus, open regedit.exe and check the registry for any names that look like ad programs, known viruses, etc and delete them.

Can you start the computer in Safe Mode With Networking, then run an online virus scanner?

Thanks for the advice, I'll try it.