Disabled DEP in Vista-computer won't boot up

Hello,
I am running Vista 2007. The DEP was driving me crazy so I ran the command to have it always off. When I restarted my computer, it would not boot up...not even offered the safe mode for boot up. Clicked the repair button and the computer stated there was a problem that could not be fixed with this application. Options clicked up and I hit "restore to previous function". It told me the restoration was successful, but when I rebooted the computer, I got the same thing. HELPPPP! There is nothing on the screen except the notice to start the repair as the computer would not boot up. No start button....nothing.