Gabriel,
Renaming the Lookout directory was perhaps not the best solution. When installing a program, certain entries are made in the registry (including paths to programs, dlls, etc...). Thus, renaming a directory will probably make the program nonfunctional.
Lookout 5.0 installs to a completely new directory (Lookout 5). Thus, you should not have a conflict between Lookout 5.0 and previous Lookout versions.
Your best bet is to uninstall lookout 5, rename the old 3.8 directory to the previous name, uninstall all old lookout versions and then reinstall.
Most of these steps you should be able to do under Add/Remove Programs. However, it may be necessary to manually delete the files, delete the registry keys and run msiexec. First, however, try to
uninstall through Add/Remove programs.
Overall, it sounds like some corruption has occurred. It would be best to try to get as clean a computer as possible and try to reinstall. Let me know how it goes.