Disable any addons you have, the 4.01 patch has blitzed a load of addons and until people make new blizz-friendly ones, your going to have to manage without, 'Cept Recount, that still works fine, not sure of any others,
if this doenst help, post back with your system details for us
The best way to apporach this is by accessing the addon folder and moving whatever add-ons you have installed to a temp folder. Try running the game again if the problem still exists, then perhaps it's something internally (drivers/software from your PC)
If the problem goes away, try moving one by one and add-on to see if still runs. Next time perhaps it's best to post PC specs before anything so your question can be answered hastily.