I have the same problem. XP
I went away for a week. I was logged out of windows XP, but the comp was still on. When I got back it was in a hibernation state, but I couldnt wake it. I hit Ctrl Alt Del, reset, power off held the button down for 30 secs. the Monitor works fine , I get cable signal out of range, the CDRW and CDROM lights come on but the hard drive light doesnt come on, I checked all the connections and tried swapping out the RAm, nothing works this is so aggrevating . How can it just lock up when nothings being done with it? The fan comes on the Video card fan comes on, it just seems like the boot process is not even initiating. I even pulled the battery out for a minute or so hehe.
Please help Im going nuts!