Well a few troubleshooting steps from here would be the following
Safe Boot-hold down the shift key while booting, key must be held down till the gear shows up under the apple
Boot to the Install DvD and run repair disk (holding C down during boot)
-this is done in the utilities menu through disk utility
Reset the PRAM
-hold Command, Option, P and R during the boot process
As for rebooting the only way to do it from that screen is holding the power button till the unit powers off.