My dell laptop with windows 7 opens media center instead of any app

So when you try to open Internet Explorer, a PDF document, etc..., Media Center opens? You need to do a Repair setup of Windows to get the file associations fixed. At some point you either got a virus or did something to associate Media Center with every file.
 
my lenovo thinkpad laptop also opens windows media center instead of any other thing i try to open.how to fix and remove the virus.if i trying to restore the lap.it will also shows the error sdclt.exe is missing.please let me know how to do this.