#1 - Go to Start -> Run -> Type dxdiag -> Hit Ok.
Tell us what Direct X version you have. If it's not 9.0c, update it on Microsoft's site.
Actually, tell us what version of Windows, the "System Model" (motherboard model), the Processor, the Memory, and all of the information under the Device and Drivers fieldsets in the Display tab while you're at it, just to get that out of the way.
#2 - If you've changed computers, reformatted, "repaired" Windows or used a restore point, or changed graphics hardware, tell us.
#3 - No offense, but I don't really see why not being able to get into WoW is urgent. If you were running a webserver, used the computer for your job, etc. sure, but...
