Help, my computers acting weird

Hello, and i got a file from my fiend about a stick figure making software and it said "open with" i chose windows media player, and soon after that all of my files where media player files, i cant open them cause it says "Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file". And bearly anything will open   pleas help, if you wish to contact me any further my skype name is pokelego1234