|Remove the third-party plugins if you can from within WMP, then restart it.|
If you need to re-install WMP, you can download v11 for Windows XP from Microsoft here: http://www.microsoft.com/download/e...
It requires a validation check so you need to be running a genuine copy of Windows to be able to download it.
Your Windows XP also needs to be either SP2 or SP3
Don't install any third-party plugins in WMP, or any third-party "codec packs" or you will end up having to re-install it again. WMP should be able to function without any third-party stuff, and for anything it can't do, use something else.