Try uninstalling it with this link text FREE version. Follow these instructions exactly.
During the un-install process you may be asked if you want to re-start your computer, DO NOT re-start at this point, let Revo continue. You will eventually get the option to Select All and to Delete - DO SO. You may be given the same options a second time, again DO SO, do not be picky, just accept all that Revo chooses. After clicking on Finish, re-start your computer.