XP Pro warm boot hard drive failure msg

I can no longer do a warm boot (restart), with XP Pro O/S, as I get a hard drive failure msg. If I just kill the power, then I can restart the system. I have always been able to shut down and cold boot OK. System is an upgrade from 98SE, 450Mhz, 256 Ram. Opinions on why this is happening & the reccomended fix please!