Safe Mode instantly reboots into normal mode

I tried to boot into safe mode to remove an aggravating program and my computer went through the steps, loading drivers, stopped at ClassPNP.sys and the log in screen appeared. Instantly it blinked off and rebooted into normal mode. This is a Sony Vaio VGN-FZ260E running Windows 7 Home Premium (recent in place upgrade) The problem was there with Vista as well, Sony support had decided it was corrupt Windows files that a reload would fix. I assumed the new OS would fix it, but no such luck. Can anyone help me figure it out, I might really need safe mode some day.