Computer starts up all by itself

Was it doing this from the time you acquired/put it together or is this something that just started happening for no apparent reason?. In BIOS did you see any listings under Boot options dealing with Wake-On settings such as WOL (Wake on Lan) etc? Some boards also have a setting to enable/disable boot state in the event of power loss. Other possibilities include faulty motherboard or faulty powersupply I used to have a signature but it disappeared and I just couldn't be bothered writing another so please feel free to ingore this.

or faulty power switch on front of computer, where the contacts are so close together that the slightset vibration, like someone walking past makes the contacts make contact. Pull the power switch connector off the motherboard and see if same thing happens.

To add to what Richard stated there are many different Wake events that could be turned on (depending upon the motherboard). Wake on LAN Wake on Modem Wake on Keyboard/Mouse Wake on Power Restore (starts the computer after power loss) Plus some boards have the option to turn the system on at specified times. Good luck. Michael J

The machine should be connected to some sort of surge protector. If it's not, then I'd recommend you purchase one. Then, turn off the machine at the strip. No more self-starting. :) Life is more painless for those who are brainless.

"The machine should be connected to some sort of surge protector. If it's not, then I'd recommend you purchase one. Then, turn off the machine at the strip. No more self-starting. :)" Well, that's one solution (personally I'd try to fix the problem) and it would definitely work. If the computer still starts up (w/o power) then it's probably time to move. And, I'd leave the PC behind just in case. Michael J

Here is still another possibility not to overlook ... i_XpUser