Your MP3 Decoder may broken. First, Go to Start --> Run --> Type regsvr32.exe l3codeca.acm, then hit enter.
Try playing. If it works, congrats. If not, read on...
Go to C:\Windows\System32\l3codeca.acm and rename it to l3codeca.bak. Then open WMP and go to Help --> Check for Updates. This will re-download the decoder and place a new copy on your system. It should be registered and ready to go at this point, but you can also run regsvr32.exe l3codeca.acm again just be sure. That command registers the ACM decoder with Windows, many “Codec Packs“ will screw up your ACM Registration, running the command should set it right again.
If it still can't work, refer to
http://msmvps.com/blogs/chrisl/articles/10723.aspx