If your computer's folder files have changed from mp3 to exe, you have a virus.
First you must determine the approximate date the problem began.
Open search tool in your start menu.
Enter "system restore" in the search tool.
When you find the folder that contains System Restore, click an icon that will open the program.
Enter a date prior to when your .exe problem began. This should restore your computer to it's healthy state. xx

If System Restore doesn't work, try downloading AVG(free), update it, scan your computer. It's worked for others: AVG Free Advisor: AVG Anti-Virus Free

To get your files back, you will probably need to run a file recovery program. Follow the links in this thread: File recovery advice!

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If it ain't broke, fix it till it is!