What might be wrong with the power option control for my monitor?

I have Windows XP, Home edition; my computer is a 2002 Gateway 500XL; and my monitor is a 22” Samsung that I bought in 2009.

I have my Power Option set so that my monitor turns off after 10 minutes of user inactivity.

The setting works as it should for awhile after I restart my computer, but eventually my monitor is instantly turned on again after the system tries to turn it off.