DVI connection goes blank upon booting into Vista

Hi all,

I am using a LCD monitor with DVI connection and has worked hassle free for
the last year. However after leaving my computer sit there for a couple
hours, I find that there is no signal to the LCD monitor. I reboot and hear
the windows start up sound but no signal.

I changed from using DVI to VGA and no problems. But why would my DVI
connection not work all of a sudden? I can boot into safe mode using DVI,
then remove the ATI drivers and can boot back in normal mode using DVI but
after re-installing drivers it goes blank again with DVI upon bootup into
Vista.

I had made no driver upgrades or added any new hardware recently. I am using
an ATI Radeon X1950Pro card with Acer WS LCD.

Any suggestions?

Thanks.