When you right click on a machine, in the GSS console, and go to Advanced and then Power Control, the options under there no longer work.

There is no error message associated to this issue.  The Power Control options simply stop working.

This issue could possibly be caused by a corrupt database.

What you first need to do is enable axengine logging to level 7.  Then run your Power Control option again.  What you're looking for in the axengine.log file is for the axengine to be scheduling and running the job.  It will look like this

Request=LiveEvent

Event=PowerControl

Type=Reboot

User-ID=0

SystemUser=ID=1000000

If you see this in the axengine.log file then you know the axengine is doing its job to schedule the work.  If you don't see this, then there's a good chance you've got a corrupt stored procedure within your database.  The only option to resolve this issue is to completely uninstall the product and reinstall it.  During the installation you'll need to create a new database.