The only thing you can do now is hold the power button in to force a power-out shutdown.
Windows will recover (or at least should!), if you boot to Safe Mode, allow any updates to finish installing, then boot back to Normal Mode, and do another Check for updates.
Here's my preferred methodology for installing the 200+ windows Updates in Vista and Win7...
Note - between each of the below batches of updates, reboot at least once, even if the machine auto-rebooted during the updates. After teh update, do a new Check for Updates. Add any remaining updates or failed updates to the next batch.
1) Install all 'Security Update for Windows'
Reboot
Check for Updates
(some will have failed, and some new ones will have appeared)
2) Install the remaining/new 'Security Update for Windows'
Reboot
Check for Updates
3) Install all ordinary 'Update for Windows'
Reboot
Check for Updates
4) install updates for IE8 - but NOT IE 9/10/11
Reboot
Check for Updates
5) install all other updates EXCEPT .NET ones and IE9/10/11
Reboot
Check for Updates
repeat 5 until there's nothing left in the main window except the .NET and IE upgrades
6) Install all Security Updates for .NET - but nothing else
Reboot
Check for Updates
7) Install all other .NET updates
Reboot
Check for Updates
8) Install IE10 if offered - IE11 should wait if it's still an Optional update.
9) Install the IE10 updates, then install IE11 and update that.
