Ariel said best as you are best to just uninstall and re-install.

However, if you still have the files (are they in windows.old)? Or did you reformat and move them? If you still have the FFXIV folder with all files contained, you can try making a shortcut to the ffxivboot.exe file and placing it on your desktop. This normally works if you didn't lose any of the files in the process, so if it doesn't, you will have to do a full delete / uninstall, and re-install, which I suggest you go ahead and do anyway to be on the safe side.