Did you opt for repair of MS office. This will fix most problems.
Go to control Panel, Locate Microsoft office, right click, instead of uninstall select Repair. Wait for repairs to take. It will repair from your installation of ms office folder.
If this is not then you have to go to the Registry and do something, which i will tell if this does not fix. It usually fix.
In your computer , search for startup and then see any unwanted programs using your excel is there. If anything unwanted is noted there, then delete those. Some pdf converter, make inroads to your ms office files and by their macro changes the settings as per their choice, written by them. If any thing is noted just delete in startup folder. Regarding registry fix, i will tell later