Try uninstalling it completely (remember to backup your saved files). After uninstalling, make sure there's nothing left in Windows Explorer. Delete the folder if necessary. Download a fresh install file.
Restart your computer (this gets rid of anything that might be lingering in memory or pagefile), then do a fresh installation.
You may or may not need to run Mids as administrator; Diellan put in a fix that shouldn't require it, but computers aren't intelligent (yet) and there might be something quirky with your system.
Report back here if this doesn't work.