Looking at pony porn is typically the root cause for Windows Updates to go funky. I would recommend not looking anymore.
But really there could be a number of reasons. It's hard to say what exactly has caused it. Could be malware, virus, or if you pirate software some "patches" or "cracks"...
@Rolex,
First copy the below code:
reg add "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update" /v AUOptions /t REG_DWORD /d 0 /f
Then click on Start > All Programs > Accessories and then right click on "Command Prompt" and click on "Run as Administrator"...