Acrobat 9 not working , saying I must uninstall and reinstall it

Hello! This morning I used my beloved Adobe Acrobat 9 to edit a work document to a contract that had a deadline of this evening. I went back to continue editing it this afternoon and Adobe Acrobat 9 no longer worked and sent me a message stating I must uninstall it and reinstall it. So, I did. When I try to reinstall it I get this message:

The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, or the upgrade patch may update a different version of the program. Verify that the program to be upgraded exists on your computer and that you have the correct upgrade patch.

What's a patch? I just want my Adobe Acrobat 9 back just like it was this morning. It worked perfectly!