Game won't run!

Hey everyone!
I'm having a problem with my game not loading up. It says the DivxDecoder.dll is missing or something. I DL the client via bittorrent and it runs great. even if i exit out of WoW and go back in, it works. I left my PC on for a couple days, and day after day, it worked fine. Wasn't until I actually turned of my comp it seems to not work after starting. Please help! I love this server and would like to continue playing. Thank you.

Install Direct X. Google Direct X redistributable and install it.