Showing Source code instead of running the file

Hii,

    today i am facing an issue in running the file the problem is ....i am uploaded my site at server and after uploading default page is not running and second one is it is showing the list of all the webpages.......

and while moving to pages through the URL than it is showing all my source code in browser instead of ruuning the file 

Please help me from out of this .