I was messing with the registry settings in
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Excel\Options
under options the value was 57 and I changed to different values to see what the outcomes would be. Excel started to glitch out so I deleted the options REG_DWORD and I restarted my machine. When I logged in I couldn't open excel documents by double clicking on the icons. I could however open the documents via file > open or ctrl + o. But excel would startup like normal, it would just be grayed out without any cells.
I thought that I had messed up my excel for good and I would have to repair it by uninstalling and installing again.
But all I had to do was go back to the regedit in the tagline above, and change the Options DWORD value back to 57 (it reappeared after I restarted my computer), and everything went back to normal...
Morale of the story, don't go deleting registry settings/changing values just to see what they do...