Monitor no signal help needed

hello all.
I don't know if I have posted this on the correct forum, but it's all visual isn't it.
Ok, My Daewoo flat screen monitor has started to just go blank after a few hours of working on the p.c.
It goes black, and then a message appears saying "No Signal", ten it turns off.
I have plugged the monitor to my laptop and it worked ok.
What could be the problem?
Is it a graphics card problem? I have an Nvidia 128mb agp card,
Sometimes I can work for hours until this happens, however a month ago the problem repeated itself quicker and quicker happening all the time. I reformatted the p.c and the problem went away for a month, but now it's back. Arrrghhhhh.
Please help.
Do I need a new p.c?

Thanks all.

I'm guessing this happens while you're working on the PC itself.

I would suggest just cleaning the graphic card's fan and heatsink to remove dust and lint for starters, using a can of compressed air with the PC turned off and unplugged.

It seems like it's suffering from overheating.

You may want to upgrade your power supply too. :)

My power supply.
I have always thought that this could be a problem as I have countless devices attatched to the p.c, and my power supply is 200 or 250w.

I have cleaned the entire contects of my p.c about 6 months ago, a thorough job was done, but I suppose I could give the graphics a card another clean.

I shall report back on my findings. At the moment the monitor is staying on as I only turned the p.c on about 30 minutes ago. I wonder when everything will go black again?

It could be your refresh rate or the screen resolution. Make sure their isnt anything int the plug on both ends that could be interfearing.

I'll check the plug.
I didn't think refresh rate mattered with flat screen, LCD monitors.
and for the res I select the compatible resolutions from the monitor List mode list.