I just experience this the same problem last 2 days. After changing the resolution using the NVIDIA GeForce, the screen went blank so its like black screen and the power indicator on the monitor is blinking orange & green. At first it will do that in more or less 10 sec., but right now it will no longer show the display on the monitor.
Since I cant do the warm reboot, I need to push the button on the CPU for 5 sec to restart the PC.
I also tried press F8 during POST but there's no option for me to open it in Safe Mode, and PC will show Windows XP screen after that it went blank again showing black screen and the power indicator on the monitor is still blinking orange & green.
I dont know what shoud I do with my PC right now.
I will try Joy's solution and hopefully it will work.
I'll update you guys!
Have a good day to all... =)