uldL73vmGHA.2372@TK2MSFTNGP04.phx.gbl,

Go to Control Panel and click on Administrative Tools.
Double click Event Viewer.
Right click Application in the left hand column.
Select Properties from the menu.
In Applications Properties, click on the Filter tab.
On the Filter page, remove the check mark from the box next to
"Information".
Click OK.
Click on Application and you should now see a filtered list
that only shows errors and warnings.
Look for entries that were created around the same time you ran
Disk Cleanup.
Do the same under the System branch.

You may find a clue contained within those error messages that
you can then use to run a Google search to see if anyone else
has had this problem.

You might also want to do the following:
Right click My Computer and select Properties from the menu.
In System Properties, click on the Advanced tab.
On the Advanced page, click on the Settings button in the
Startup and Recovery section.
In the Startup and Recovery dialog, remove the check mark from
the box next to "Automatically restart".
Click OK twice.
Doing this may prevent your computer from restarting and will
instead display a blue screen with information that you can use
to troubleshoot this issue.

Good luck

Nepatsfan