Many have pcs\monitors that go down far before that,but usually right after the 1 year warranty is up, go figure. My first suggestion to you is to try the monitor in another pc, or try another monitor in your pc. So if anyone you know has one...
Did you or anyone possibly install, change settings or add any components recently? Is your cable tight?
This could be a number of things, a bad display cable, motherboard problem, graphics card... onboard or otherwise...OS problem...
Also, I assume you have XP and a CRT monitor, not an LCD.
Paul