Computer help!
 

My desk top recently crapped out on me. Now when I press the power button, it goes on for a split second and then goes off, on again, off...I know this because the fans and LED spin and light up for a second and then go off. Once the pwer button is pressed, this on/off thing will go on indefintely if I don't use the switch on the back of the computer to shut it off. Some digging around tells me it could be a bad power unit or a motherboard. Utterly clueless if it's the MB.

I'm not good when it comes to computer hardware, but if I know what needs to be replaced, I can easily get the parts and fix it myself. I've never really had to fix a computer before. Right now I'm using either my laptop or my ancient desktop that's sloooooow.

could be an overheating issue

try blowing it all out with ionized air. get a can at the computer store, get all the dust hair whatever out.
make sure all of your fans are running fast, not just turning, there will be one on the main porcessor, maybe one on the video card processor, one in the power supply and possibly also a general case fan.

beyond that maybe check power supply and blow it out if you can, ive replaced two of those on mine, the small fans on the processor, video card and power supply are as cheapo as they can get away with

Either power supply or Motherboard, more likely the former than the latter. I had this exact same thing happen with an old eMachines unit I got for free. As Lutz mentioned, manufacturers cut costs wherever possible and power supplies are one of the first on the chopping block.

It could be many things as well as those most likely suspects listed above. My first port of call would be an internet search including your computer's model number and the fault... you never know it might be a common problem.

You really have to do a process-of-elimination repair on that one, it could be a four different things. Swap in a new power switch first, then if that isn't it, next thing is the power supply, if that isn't it, it's the motherboard, junk it.

Power switches are "moment" type.

I actually would not think it would be the power supply, usually the power supply is an either dead or alive thing. Since it comes on for a moment, I suspect the switch. If it has any contact problems at all and is passing current even for a millionth of a second beyond the let-go point in the moment switch, it will make his PC do exactly as he described. I'd just get a push button moment switch at Radio Shack and jumper it in place of the onboard one to test it. If it comes on, either use the RShack switch or use it until the computer can be swapped into a new case.

A bad power supply is usually the result of poor fan maintenance, the thing just finally cooks and dies, or bad solder joints from the original build, again something that just makes it fail.

coudl be that the reset button is stuck. Fixed a problem like that on my sis' computer a while back.

Good point. Easy fix on that, just follow the reset button leads back to the MB and disconnect. If PC comes on, that's it.

I'm going to say motherboard since it powers on.

However, try removing peripherals like the video card,etc and see if it isn't them.

I've been spoiled by beep codes on computers. Bad power supply, ram, video,etc. Makes narrowing down a bad component SO much easier.

Oh also inside the computer I would try pulling the CMOS battery with the computer unplugged. I've had bad bios saves screw with me for countless hours.

If it's a cheap clone it's the power switch or reset, I've seen it a million times, I've replaced hundreds of these switches over the years - these white box clone boxs are utter cheap junk. The contact breaks up, and now you've got metal floating around inside the moment switch.

Never thought it could be the power button, but then again I don't know much about computer trouble-shooting. I'll look at the reset button too.

My computer is a generic brand that I bought off Craigslist from some guy who builds systems. This was a couple of years ago. It has the see-through side panels with swanky LED fan lights.

Most likely it is the power supply. If it is a Dell/HP/E-machine/Compaq, toss it if it is old (3+ years) If it is a "normal" PC with normal standard parts inside, replace the power supply with a decent one, and carry on. The on/off blip is very common for failure of the power supply. I see it all the time. Maybe 20% of the time it ends up being the motherboard, but far more often it is the power supply.

Stupid question, have you tried unplugging the power cord from the power supply, letting it sit for a min and trying to power it back on?

I'd wager power supply over anything. Can you see a brand name on the power supply?

EDIT: Actually yes. I'm going to say its definitely the power supply.

Reason: When the power supply turns on, it sends out a pulse on the grey-line of the main ATX power connector to the motherboard. This will tell the motherboard if the power is clean and good, thus OK'ing the system to fully power up. If the signal is not good it will..not turn on.