If you are using a shareware version you might not get much support. I would still try to contact them first.
Personally, I would just delete the windowblinds directory. Then go to add and remove programs and click windowblinds. It will ask to remove the association because nothing is there. If you have a registry cleaner, that is the best way to get the left over registry associations. I would then perform chkdsk on your drive and defragment it as well. Click the start menu, go to run and type chkdsk C: This might be the reason the installation is having a hard time. Your hardrive might be a mess. You might have all sorts of other problems such as spyware too. Try searching for Spybot. It is a free registry cleaner as well. The best solution might be to dump the hard drive and reinstall windows. But, you might also have a defective download. Windowblinds is a great program, and it works flawlessly on a good operating system. It works great on mine. Good luck.