No signal to monitor after resume from sleep

I’m currently using a desktop which has a AMD cpu and an ATI graphic card, I have opensuse 12.3 installed, and there is no signal after I have put my desktop into sleep for about 3hours, I can’t resume from sleep. The desktop is working, and the fan is on, but the monitor just don’t have signal. I have unplug the HDMI cable, and it still does work. It works only if I restart my desktop.

Can anyone help me?