What exactly happens when you attempt to open a project file? Does LabVIEW simply hang, or is there an error message, or what? Are you able to create new projects?
It might be worth repairing LabVIEW. To do this (assuming you are on Windows), go to the Control Panel, then Add or Remove Programs, and select National Instruments Software. Click on change, and then find LabVIEW 8 and select repair.