Monitor sleep in Windows XP does not work. Is there an add on to force it?

Monitor sleep in Windows XP does not work. Is there an add on to force it?

I have an EEE box with XP Home and a DVI connected TFT, and it does not sleep the monitor. It only starts working after I go to the energy control panel and turn it off and on again. Then the timed sleep works for the current session of computer use. After a shut down and boot next day, sleep does not work again (it is still set in the preferences however).