Monitor flickers on and off

My monitor flickers on and off. It happens most often when I turn on my pc. It also does it when I'm surfing the net and reading my mail. It doesn't do it when my kids are playing games. Sometimes...when I first boot up....it will flicker so much that the screen will come back distorted and freeze up. Sometimes it will also put the monitor into sleep mode if it stays off for more than a couple seconds. Then it suddenly flicks back on.
I have replaced the monitor with a spare...and it still did it. So it's not my monitor. I'm thinking it may be my power supply? I'm running Windows XP....and my pc is only 1 year old.
When my computer has been on for awhile....this problem seems to stop. For the last 3 days I haven't turned my pc off....and it hasn't flickered. But I know if I reboot....it will.

Any ideas? Thank you

 

If it was your power supply, then its more likely that the PC would reset/switch off.

More likely to be the video card, perhaps it just needs to be re-seated in the slot?

 

I'll try re-seating the video card tonight and see if that works. It also flickers more often when I use my mouse scroller button, again though, mostly when I first boot up. When I first boot up, it flickers everytime the pc tries to load a program, like Norton...mail.....etc. This is what made me think it might be the power supply.

 

Have you checked the monitor's refresh rate?

Video drivers updated?

 

I have updated all the video drivers. The monitor's refresh rate...no I haven't. Where do I find it....and what should it be set at? What does the monitor refresh rate actually do? Sorry, I'm "duh" on this subject.
Thank You

 

The number of times per minute that a computer monitor screen image is renewed. A fast refresh rate makes a screen easier to view and is much better for your eyes. Good monitors have a refresh rate of 70 to 75 hertz per second or higher.
To help with prevent eye strain we, users have there CRT monitors set to refresh rate of at least 75 Hertz.
LCD displays do not have a refresh rate, however if you need to set a rate values of 40Hz or 60Hz can be used.

How to change refresh rate:
http://www.computerhope.com/issues/ch000558.htm

 

Thank you for your help. I will check my refresh rate this evening. Would the refresh rate suddenly cause the monitor to flicker on and off though?