You could try running the install for 6.4 and see if that fixes it. There's a download for it here:
http://oldversion.com/program.php?n=wmp
You might want to also download 7.1 from there just in case there was something wrong with the one you previously downloaded. I tried both the beta and the final versions of WMP 9 and I won't touch them again. You'd be wise to stay away from them.