windows media player won't open

I would be very grateful if someone could help with this problem. I am running vista and media player 11. According to the computer media player is fully updated and present. I can find all the folders and files but I can,t get it to start. When I try to run napster it says I require windows media player.

This is driving me mad and I can't find any solutions elsewhere least of all through microsoft. I have tried system restore and have found out I can,t uninstall and reinstall so am out of ideas.

Thanks in advance for any suggestions