Player plays media too fast

Both video and music play too fast Can you help?

I have the same problem on a PC with Win 2k.
On another PC with XP it works perfectly.
WMP versions are the same (the last version)
On XP, viewing at full screen and clicking with the right mouse button appears a menu which allows you to increase or decrease the video playing speed.
On win 2k this menu doesn't appear even if in its online guide this function is shown...
I don't know how to solve this problem.
Anyone has other ideas?
Thank You

Gerpa