"previous installation is in progress, do you want to udno the changes?" what the

whenever i try to uninstall something, a message pops up that says something like "a previous installation is in progress. you must undo the changes." and then i click "ok". the uninstaller freezes, and now i can't uninstall anything (unless the uninstaller realy would take more than 3 hours to undo changes) how long is it exactly? i already waited 30 minutes. how do i take this out? thanks in advance!

 

never mind i fixed it i just had to install a program that i tried uninstalling agian