PC WONT BOOT PLEASE HELP..

One time I turn it on nad doesnt boot up,after a few hours after work I try to open again my PC and blue color displayed on my monitor telling me an error message: DRIVER_IRQL_NOT_LESS_OR_EQUAL .and i try to restart but wont work,PC wont boot up,no beep sound.I repeatedly do this but then again pc wont boot.PS Fan is working,DVD-RW led is light on and working.I try to boot up from my XP cd but it doesnt work,too.
Specs: Intel Celeron 2ghz,512MB RAM,built-in videocard/soundcard,20GB primary(software/progrms),80GB(data storage),I recently replace my monitor to a LCD TV monitor..I did some configuration on my computer a week ago before this problem happen.Please HELP ME!Thanks a Lot!