How to make File extensions show

hoop__it__up

b4 i could see the extension of the files and then i checked it out and now files have no extensions i think i changed it in start--> run--> and typed some command that i 4got lol where it allows u to take out start up programs and also there was an option to see or not to see file extensions Thnx

Webmaster

My Computer - Tools menu - Folder Option - View tab - option :Hide extensions for known file types.