My hp w2207h goes to sleep

new hp w2207h goes to sleep as soon as we turn it on if you disconect the cord to it check video cable I have a similar problem. My HP w2207h is being used with a Dell Dimension 4700 about 5 years old, running XP. If I turn the monitor off with power button, when I return after, say, a half hour or so and turn it back on, the screen is black, a pop-up box tells me there is no VGA signal and no HDMI signal. Then, another pop-up box tells me the monitor is going to sleep. And I can't figure out how to wake it up except by turning off my pc with the power button, something I'd rather not do, and restarting the pc.

I tried the solution suggested by jhayssonne and thought that might have solved it, but it is still doing it. A long time ago I changed my power saving options in control panel, too, to always on.

any one have a suggestion? Thank you.