machine turning on and off by itself????

I have this machine that will in the middle of the night turn on and try to boot up and then shut down and boot up and it goes on and off like that until I unplug the ac cord.

I installed a new power supply but the connections were really poor as cords were real short. (Did the old paperclip test to see if fan turns power supply on and that turned on fan in both the old and new supplys). Tech suggested power supply was working in both the old and new but not positive.

Now just the blue power light turns on and doesn't boot to software. Put in old power supply and it logged onto windows and I was using explorer and surfing the web. Logged off and was never able to boot again. (only blue power light goes on)

Any ideas as to cause or should I look for a recycle bin? Do people buy these old towers?

Could be several things but the most likely that come to mind are hardware problems. It's possible your MOBO went bad. It's possible there is a short in the case wiring. It could be overheating and shutting off. If the power supply's own fan is spinning then I would NOT suspect it is the PSU.

How old is the machine and is it still under warranty? If so call it in and get it returned ASAP.

Generally you strip them down to just the basics PSU, mobo/CPU/fan, RAM + monitor (no case connectors attached) then use a screwdriver to start and see if you can POST. If no beep then it is one of those three. If that works add HD and see if you can boot. Shutdown and reconnect case wiring - try again.

On the lighter side of things... it could be a poltergeist!

When I was first married back in the late '70s, the first house we bought had a poltergeist. It was a minor nuisance for the 9 months we lived there, then we bought another house and rented the first one out.

Sorry, off topic but I will play along for a post or two ...

Well I had a motherboard once that would loose contact with my video card when it got warmer. Talk about a Ghost in the Machine; that was a bugger to figure out. And the solution was a wooden stake through it's heart ... well really just a wooden pencil between the case and the MOBO to keep it from contracting and popping out the video card.

I knew you thought of your ex as a witch but I didn't know you had ghosts too. Halloween must have been fun at your place.

As I stated, on the lighter side... sheesh you're such a "hall monitor" sometimes!

I promise I'll be good TM, 'till the next time I feel ornery! LOL!

Sounds to me like his problem may be a faulty motherboard. He might also have a Wake On LAN feature enabled too in the mobo's BIOS settings.

He can take the power supply to any good computer store and they'll test the PSU for free.

Still sounds most likely a motherboard or faulty wiring / switches in the computer case itself.

I would look in your BIOS Setup Menu for any "Wake on..." settings you don't use - for example, "Wake on LAN" which allows a signal from the network to use your network interface to wake your computer.

Also, note an oversensitive mouse may detect movement from footfalls or other vibrations. It may be necessary to turn the mouse on its back when not in use.