PC keeps turning itself on and off!

  annie1206 10:33 10 Jul 07

my PC recently has been taking ages to turn itself off, then a couple of days ago, i turned it on and about 10 minutes later it had turned itself off! then yesterday it came on, on its own, then off. i turned it on and it stayed on. then last night (due to a leak in my bedroom!) i slept in the lounge and woke up to my PC coming on, going off, coming on, going off, but only the fan starting up, not actually booting up! i'm confused, i'm not very PC minded!

  Gongoozler 10:39 10 Jul 07

I think your PSU might well be failing (or have failed. Fortunately these are not terribly expensive or difficult to replace. If it isn't the PSU, then it could well be the motherboard but you need to be more "PC minded" to replace that. In either case there's plenty of advice to be had on this forum if you want to tackle the job and have access to another PC while you are doing it.

  annie1206 10:53 10 Jul 07

ok i'll look in to those things, yeah i have my laptop. is the psu generic?

  Gongoozler 11:14 10 Jul 07

In general, yes ATX PSU's are the same shape and size. You do need to make sure the new one is at least as powerful as the old one. Unless you have a very powerful graphice card, then 400W should be sufficient. This is a fairly typical PSU that should suffice click here.

In diagnosing your problem, keep in mind that the process of switching power to the computer consists of the power switch which have contacts that connect while the switch is pressed. This connects two pins on the motherboard. The motherboard then connects a pin in the PSU to 0 volts which starts up the main PSU functions. The PSU fan will then run even if the PSU is not generating all the voltages. The motherboard fans will only run if the PSU is correctly generating 12 Volts. The motherboard also requires 5 Volts and 3.3 Volts to operate. Deciding which of these things is malfunctioning is what requires a bit of PC knowledge and willingness to experiment. The switch is unlikely to cause the computer to switch on and off on its own. Motherboard faults rarely cause random switching on, more often if they have a fault like this they will switch on and off while you are using the pc. The PSU has power applied all the time, and although the operation you have described is unusual it is possible, and as changing the motherboard has implications regarding the operating system and drivers, the PSU is the easiest to try first.

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