How about trying to google that?
I mean for sure You're not the only who has got this problem. There might be a few reasons causing that.
Also You can try on jsp wow subforum located here:
http://forums.d2jsp.org/forum.php?f=210Random googled answer:
Windows Key + R

msconfig

safe mode, shutting down all process [ not microsoft ones ], turnin on system and then patching
/
Quote (iDGames @ 3 Jul 2011 23:25)
Disable your firewall and all anti-virus programs. Then run WoW again.
As said above. Do it first. If won't help then keep googlin or try my method. However it's random googled so I'm not sure abot this!
This post was edited by Wrona on Jul 3 2011 03:30pm