Monitor problem - "no signal"

I've had a problem recently with my monitor going to black and the screen giving the "no signal" message.  My computer is a Dell, but it was a gift so I don't have any specifics on the system info other than what I've displayed below.

The monitor goes off and displays the "no signal" message after I've been on for several hours, so it does work for a time.  However, when it does this the CPU seems to keep on working as usual.  There are no beeps, or other noises that would indicate that the CPU reacts in any way.  I believe it to be a problem directly with the monitor, but I'm not 100%.  When the monitor goes out, the only way for me to get it to work again is to power off the computer and turn it back on.  Everything works like it's supposed to when I have to do this, but I hate having to power things off and on this way as I know it doesn't do the computer any good.  I have checked all of the cable connections, but everything checks out.  Since the monitor doesn't hook to a card and the cable connection is 'hard wired' to the inner workings of the computer, I'm at a bit of a loss.  Any help/suggestions would be appreciated.  

I use Windows XP.