Update Shield with No Action

On Tuesday, per schedule, I downloaded and successfully installed the

Windows updates. On Wednesday, I temporarily received the shield again, but

it quickly disappeared with 0% downloaded. Today, the shield reappeared and

stayed at 0% downloaded. In addition, my firewall on my AVG Pro was

deactivated, and when I tried to activate it, the computer stalled with the

hour glass and no action. I tried to open Process Explorer, but nothing.

OK, so I tried to restart the computer, but could not activate anything.

Finally, I hit the emergency button and everything is working fine, with no

shield this time. Can anyone give me any explanation. Windows XP Pro, 20

gb hard drive, 520 meg RAM.