Personally, what you should have done with Pro is a fresh install and not do an install over basic because they are two different versions and might conflict with one another, other than that, I dont see any other reason for it to screwup as you say. if on two different computers then it shouldnt harm your basic version even if you are on the same network, if Im understanding you correctly? If multiple installs are in your add/remove you'll have to uninstall the rest and stick with one version, if its opening on its own, then it may have gotten infested from the gnutella network.