There can be virus - scan your PC with all your antiviruses. Some files are corrupted - use sustem file recovery or yoiu can use special utility Windows Cannot Find Fix Wizard. See related link to figure it out.
Regedit.exe - is the registry editor. Every time you install a program, or new piece of hard-ware, windows writes entries into the registry which tells the operating system where to find the device (or program) - You should only change the entries in the registry if you know what you're doing - as it's possible to mess up the registry so bad your computer will stop working !