Go to the Start menu, Programs>LW>Uninstall.
No your downld folder won't be affected. Then re-downld the installer (choose the offline installer) & try installing again. It sounds to me like your registry needs a clean but I'm not a windows expert.
Oh & please read the forum rules which are posted at the top of every section of the forum. Too many new members are not reading them;
Forum Rules (click here) These are the Limewire sections:
Limewire Forum sections Post in the wrong place & nobody will answer your thread.