Computer (sometimes) won't power on

I've been having this problem for a few days now. Most of the time when I press the power button, nothing happens. Sometimes (especially if I haven't tried in a while), the power LED comes on and the fans start to spin for about a quarter of a second, then it's off again. And occasionally, it powers on normally and functions just fine (except it powered off suddenly after I entered my password to log into Windows the last time I had it on). Unplugging and plugging back in the power cord, or SATA cords, or a PCI card seems to make it more likely to come on, but only once.

I really don't know what to make of it. Does anyone know what to think?

 

My first guess would be a failing power supply. The fact that it starts and runs sometimes with no problem seems to indicate that the basic components are all working but it isn't getting a steady supply of power.

How old is the machine? If it is from a major company like Dell or HP then it probably came with a minimal power supply that deteriorates as it ages.

 

I built it the machine myself, and the power supply is less than a year old. I was never really sure if the PSU I bought was powerful enough, though. Could that be the cause?

 

We can see if anyone suspects anything else. It is just that the fact that you get no lights or fans when it doesn't start up just seems to point to power. Even with a bad CPU or BIOS problem you should get a power light and probably fans. After your password is entered Windows would start using more power as it goes into full startup. Double check that all your power connections are firmly seated.

Give a quick look at a power supply calculator to see if you are in the ballpark. http://extreme.outervision.com/psucalculatorlite.jsp (or google for others).

 

It could be a bad power switch but I don't know the troubleshooting steps for that. I'm sure someone else can give you pointers.

 

I used one of those calculators after I first built the machine, and I seem to recall that it indicated I should use a PSU a bit more powerful than the one I have (650W). On the other hand, the last time it turned on was while I had the video card, PCI sound card and a wireless card removed. This morning I dug out my wattage measuring thing I bought a while ago and never used, and it indicated it was using only about 150W. I put the video card back in and it hasn't powered on since, so I haven't been able to measure it again.

Anyway, a faulty PSU does sound likely, though the little LED on the motherboard itself indicating that it's connected to a power supply is staying lit up... if that makes any difference.

 

Let's see what others have to suggest.

Power supply was just my guess. 650w and a year old should power most machines, so I may be off the mark.

(The red light doesn't take any real power so that just says the PSU isn't totally dead which we know.) Do you have another PSU around to try? Even if it is less wattage, if it powers up the machine then you know it is probably a power problem.

 

Unfortunately, I don't have really another power supply around to try using, or I would have already. I'm thinking I'll have to take the PSU to a computer shop tomorrow to see if they can test it. Unless I get any second opinions first.