Losing VGA signal

Hello Im new here but have been seeing alot of links directing attention here so I thought I would check it out. I have a problem with losing a VGA signal. It started happening when I purchased a new video card. Radeon HD26000 XT to be exact. My system is a Compaq Presario AMDx2 4200 Dual Core. 3MB memory, 160 gb hard drive.
I tuned the graphics card with ATI catalyst to go beyond the clock setting. I only went up appx 30% from factory setting. I tested it with the catalyst and it passed. When I play my games all of a sudden the screen will go blank and display a "no vga signal" across the screen. No response from any other commands. I tried to analyze this by tesating the clock config and when doing so on the "auto tune" setting via catalyst the screen would go blank half way through the test and I have to shut it down again.

What could be causing this? My monitor is a 17" HP LCD monitor. Does the monitor have anything to do with losing this signal? or is the card just a bad apple?

thanks in advance..