install/uninstall issues

I have wb8 installed with a trial version. When it expired, I tried to uninstall it and install wb7 since I had a license for it. Now wb7 doesn't work, it keeps telling me that it didn't install correctly, and I can't get rid of the skin that was applied by wb8, because it didn't remove it when it uninstalled. (Seriously?) I use a dark skin most of the time, but I need to use a light skin for certain things like webexes and now I can't, rendering my system basically useless to me. There has to be a way out of this.