I NEED HELP -

Some how my all my .exe files were reset to load by srcds which i think is a
gaming program. I try and load programs when it was like this and it said the
dll failed to lauch but i realised i can change it (only to programs e.g.
internet,notepad,word) i have changed it to notepad and alot of gobaldy goop
came up. I want to know how to reset it back to normal (which i gather is the
computer itself)
Please reply asap thanks in advance
andy