The File wmp.dll has , problems

My computer runs with Windows XP SP2 and the RAM size is 2GB. The motherboard is Foxconn G31.
Every time I am trying to open Windows Media Player an error message pops up. ‘The File wmp.dll has , problems’. Also I am not able to install Media Player 9 because of the error ‘Latest version is already installed’ and got quit.
Please help me to fix the problem.
Thanks in advance.
