Dell Vostro 220 - Power save mode on monitor

Hi, this is my first post on this forum.

I run a Dell Vostro 220 with windows Xp 32-bit. I have a nvidia GeForce GT 430.

Recently when using my dell desktop, i have been playing games. After either a period of minutes or hours my desktop will spontaneously go into power saving mode. I cannot exit from this mode by pressing keys or by pressing the monitor on or off again. However on this mode, i can hear sound. I noticed this a couple of weeks ago and have had this desktop for about 5 years.

I have tried to look online at solutions but they never seemed to solve the error. The solutions i tried to do where these:

- Dust insides, this had no effect on my PC

- Check the monitor to see if power cable loose

- I have also checked to see if my graphics card is exceedingly hot but it operates under what it should.

Generally these errors occur on games that are more demanding of your graphics card. I have had no problems other than when i have been playing games for the desktop. I have exhausted all possible solutions and it would seem that it isn't a hardware problem and i was wondering if any of you may have a solution to this annoying problem.

Thanks :)