Monitor help needed???

Here's the deal.......

Whenever I turn on my PC (Windows XP) after an extended period of being turned off (hours) the monitor takes about 20 minutes to display an image. I hear the normal Windows start-up tones but I get no display.

I had one of those home services come by and I had an extra video card so they replaced it and still the same problem. All diagnostics show that the monitor and video card are fine and the PC is free of viruses etc. The monitor also worked fine on another PC and the images are perfect when displayed. Everything functions fine with no lag once the display appears and re-boots do not re-produce the problem. It's only when I start it cold.

Any ideas???????

Thanks for your time.