Does this sound like the power supply

[fla]

My dev PC sometimes won't turn on, not a sound. If I turn off the small switch on the back of the power supply and turn it back on while holding the PC's front power button it comes on normally. This only happens if the computer has been off for a long time like more than 24 hours. Once on, the computer runs perfectly forever until I shutdown. No hardware has been added to this PC since the graphics card and power supply were upgraded over 2 years ago. The problem turning on only started two weeks ago.

Is this a power supply or power switch issue or other? Any ideas other than leave the computer on forever...

BTW I tried turning off the power supply switch after a shutdown in which case at the next power up 24 hrs later I couldn't even turn it on with the above workaround. Took 10 minutes of playing with both switches.

[whurlston]

Could be the power supply but it sounds more like either the switch or the power controller in the motherboard. You will need to use a process of elimination to find out.

Disconnect the power switch and use jumper to momentarily short the pins. Just use the jumper to make contact between the pins and then remove it. This will simulate the power button being pressed. If it still exhibits the same behavior, try another power supply.

You can also try setting the motherboard to power on whenever power is restored and then it should automatically turn on when you turn off the switch in the back and turn it back on. In the bios there should be a setting for resume after power failure with the options of "on", "off", "last state" or something similar. If it is your case power switch, this will solve it.

[Torque]

I had a motherboard that behaved the same way. It was one of those that had the bad capacitors (the mixture of the fluid that is inside of them was incorrectly mixed or something) that affected a number of motherboard makers.

After doing the same thing you're doing now, it got to the point where I'd have to take the CPU out, give it power, then off and put the CPU back in for it to turn on. I found out it was still under warranty so I RMA'd it. Never had the problem again.

[zaphod7501]

Similar to the BIOS setting for resume after power interruption would be the resume on alarm, where you set a specific time of day to turn on each day. One possible situation here is that sometimes this setting needs 24 hours to activate the first time. (24 then next timed request)

The BIOS turn-on should eliminate the possible bad switch option.

Given my recent experiences, I can suggest a few other options. A card that shifts in the socket can stall startup. (My Hollywood Plus card stopped one of my PCs from booting properly - last week) Reseat all cards (with power cord disconnected). A bad hard drive can freeze the boot process (my repurposed 80Gb drive just died after many years of use and took a power supply with it - two days ago). And of course a power supply can just die (yesterday).
(not all the same PC )

[bgowland]

Similar to Torque's response, my initial thought was a breakdown of a capacitor somewhere in the system. Whether it's in the PSU or on the mobo as part of the 'soft' power circuitry is hard to tell.

I'd probably take the front panel power switch out of the equation as most of these are what I'd refer to as 'momentary' switches, i.e., they don't latch on/off and only make a connection (or break a connection) when pushed in. If you can get the system to start when holding the front panel switch, it suggests the switch is making/breaking contact as required.

Cheers,
Brian

[fla]

The pool of knowledge on this forum is superb, thanks for all the replies! I just set my bios to turn on after a power failure and the PC does turn on after an off/on cycling of the power supply switch but since the PC hasn't been off for 24hrs, the front switch also works to turn on the PC.

Tomorrow if the front switch doesn't work, I'll try cycling the rear switch and if that works then I'll simply always use that technique to turn on the PC. I'll also open up the PC and make sure all the cards are well seated.

[stustunz]

another thing is just unplug everything off the motherboard then plug it back in(all connectors)
sometimes the contacts of the plugs no longer make a good connection

[pBS]

hmmm,why did you have to replace the power supply originally? usually things that make the PS fail will damage the MB also...but capacitors don't always fail immediately, so i'm thinking your MB also took a hit and is just now failing...

the switch is most likely ok, it's probably the charge cap for the switch transistor on MB..unfortunately means replacing motherboard..

[Deusxmachina]

another thing is just unplug everything off the motherboard then plug it back in(all connectors)
sometimes the contacts of the plugs no longer make a good connection

Or they're just plain loose and not noticed. Make sure the 4-pin (sometimes 8-pin) CPU plug is in fully, as well as the main 20 or 24-pin plug. I had one like that, was hell to boot unless already warm. It didn't work right until I heard the big "click" while pushing in the 20-pin. Swore it was in before that, but nope.

[fla]

hmmm,why did you have to replace the power supply originally?

The first power supply never failed, I just put in a new more powerful one while upgrading the graphics card 2 years ago. I pushed everything in last night (connectors, cards...) and even checked the battery voltage. Today it started ok but it was less than 24 hours so it's inconclusive.