Sounds like a hardware failure. Step 1 is to find out if HP offers any kind of hardware diagnostic program, and if so, to run that.
If not, I would start by getting a can of compressed air, and blowing out all the fans on the system. You might also want to reapply some thermal paste/grease to the CPU. If that's an XP system, it's probably a bit old and crusty by now.
If the system continues to reboot even after all that, the power supply is likely bad, though in the past, I have seen symptoms like this turn out to be the motherboard or CPU. So if there's no hardware diagnostic program to help you pin down exactly what's wrong, and blowing out the fans and running the system with the case off doesn't help... I'd replace the power supply, and if that doesn't do the trick, you're looking at a new system. You can replace the motherboard or CPU, but it tends to cost more than it's worth investing into an old system unless it has some kind of sentimental value to you.
I i have a Hp PC.Recently i did a format of my pc and installed a fresh copy of windows XP.it was Ok for one day.Then when i powerd on the PC it showed me the black screen where it says :sorry for the incovenience....
safe mode cmd...
safe mode networking..
last known good configuration
Start windows normally
i have tried both of the last options but windows dont start it takes me to the initial screen of HP and displays for one sec this :
"Press any key to option ROM message"
then it goes again to the screen "sorry for the incovenience...".
I have tried entering safe mode but it takes me again to the initial screen with the HP logo
Please help. what did i do wrong?