acer aspire t180 o/s xp it suddenly shut dwn then rebooted then shut down again wouldn't resart it just beebs, then it would start up then shut down and beeb this person says its the prossessor one the power supply unit one the hard drive ?
Repeated starting and stopping - power up / power down is symptomatic of a power supply fault - easy to replace - a small computer repair shop may sell you a second-hand PSU at a generous discount. Do not be frightened of using a lower Wattage PSU unless you have added lots of peripherals to your machine. I replaced a broken 350W PSU with a second-hand 250W (£20) without problem.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.