Carlos, I agree with Rich 100%. MSE and Malwarebytes will give you ample protection. You can also try Avast. It works well with Win 7.
Without a registry backup, I agree that a reinstall is your best choice. But I would invest in a new hard drive first. For backing up the registry, Brink, one of the Admins here, has written an excellent tutorial: Registry - Backup and Restore
. This is a good thing to do on a routine basis. I also suggest that you image your system to an external hard drive. Macrium Reflect (free) is a good imaging program. Imaging with free Macrium
. I use it.
Thank you very much for the rep. I am sorry we could not help you solve your problem short of a reinstall. I wish you and yours a healthy, Happy 2011.