Need Help Setting TP2 Media

Ok I have a problem my mp4 movies would work perfectly with the default system WM 6.5 then i downloaded this Phillips platform player and it switched my media to that program and it did not work with it so when i erased the Phillips player i thought it would just go back to normal but now i cannot open up my movies it gives me a message that says “the file cannot be opened.Either it is not signed with a trusted certificate,or one of its components cannot be found,If the problem persists, try reinstalling or restoring this file.” I also notices it does not have the photo album default thingy it instead has a paper with a windows sign. If it just has to do with the defaults someone please tel me how to set the defaults back or if it is something else please let me know oh and when i open windows media player and open the file that way it works it only does not work when i click the file itself. And some of my music i get the same message