File Extension Problem

Hello,

I can't open any files in my computers. All files having file extension problems. This really disturbing me. I can't even open files related to windows. I can do nothing. I can't even open Internet Explorer or other basic programs in windows. I can't run or open the files that i've download. Many software I've tried to solve this problem, but it doen't work because those files can't opened. I really, really need a help.... I'm still new in this site, please help me..