Computer won't turn on at times...

[vliktor]

I haven't posted here since 2005, just coming back now as I have a major computer issue.

OK, let me be specific: the computer that I recenlty built will at times turn on, but for weeks or days at a time, it suddenly decides not to turn on. Pressing the power button several times doesn't help.. but eventually, days later, after all the frustration has passed, it will somehow already turn on.

So it's using an old CRT monitor, plus a new motherboard/HDD/dvd-rom/PSU, but an old case, CPU, and RAM. I've tried a different/working PSU, reseating the RAM, trying just one RAM stick at a time, the power cables, moving it to a different power socket, but it just doesn't work. I've even tried removing the motherboard from the case and just have it turn on by shorting the power switch jumper (is that the right term?) with a screwdriver, and it won't turn on. The rest of the peripherals (KB, mouse, monitor) are all hooked up, the monitor lights up, the optical mouse lights up, but absolutely no activity on the motherboard itself.

So thinking that this might be a PSU or motherboard problem, I returned it to the shop, twice. To my amazement, even with the same parts except the monitor, KB, and mouse, it turns on with no problem. And this has happened to me twice (!!), after describing to the shop what the problem is.

Now I have the computer back, and it works (for now), but I am just not sure what is causing this. Nothing has changed ever... the technician implied that this may be a problem with either the mouse or the monitor "shorting out" (again, I'm not sure if this is the right term) the whole system. The monitor is quite old (6 years)... the KB and mouse new.. so is this possible?

Sorry for the rant; if this thing gives up on me again, I will have absolutely no idea what to do.

 

[C1]

An inexpensive thing to try is to replace the front panel switch (should only cost a few dollars) & I think Ive seen them at Frys Electronics (around by the Fans/Misc Hardware components section).

 

[vliktor]

Yeah, but the thing is, I've already tried just shorting the Power switch jumper with a screwdriver, instead of using the power switch itself. You still think it's a front panel switch issue? I've also removed the motherboard itself from the case, to rule out a short circuit from the casing (although highly unlikely, as this computer DOES turn on after a few days), and it still won't turn on.

I really think this is a PSU or a motherboard issue.. but I'm really not sure. I'm at a loss.

 

[BoomerD]

Then the best way is to try your components in a different computer.

 

[C1]

The OP stated that "I tried a different working/PSU" plus the pin shorting eliminates the switch. The thing is that a PSU in a computer will start up without a monitor, KB or mouse plugged in.

So a test is to try is to energize without these things connected (or switch them out one by one) to eliminate the possibility of any short as cause.

If one had to guess, the order of suspected component would be PSU then MB.

 

[vliktor]

Thanks for the responses, guys.

Update: I sent the computer back to them again after it won't turn on again. When we got to the shop, it would STILL turn on (!!!), but this time, nothing came out of the monitor, not even POST or BIOS. They think this is a mobo issue, so a replacement may be in order.