motherboard - Computer does not boot, often

I can turn on my computer and sometimes it will boot up just fine. After a while of use, days or even a week, when I try to turn it on, it powers up, in that the fans spins up, the power indicator light at the front comes on (although orange, it is usually green), but it will not boot, the screen remains black and never comes on.

If I leave it for a couple days, and try it again, it comes back on, and the cycle starts over.

I have no parts for that computer that I can currently swap out to test. I have tried removing the RAM or using one stick to see if it would get any further in the process, but to no avail.

I suspect I may have a motherboard or power supply problem.

What could cause a situation like this and are there any solutions?

Edit: There is no beeping when it boots, the only thing that happens is the fans spin up and the power indicator comes on orange.

The easiest way to track what's wrong (requires some experience with computer building perhaps) is disconnecting all hardware and then reconnecting everything one by one.

So connect the motherboard with the power supply with only RAM and your CPU in. Does it do anything? Great, add your GPU or your hard drives. Keep adding hardware until everythings connected and it's not short-circuiting (which is probably the problem). This off course is a lot easier if you have an on-board VGA connection, since then you can also read the BIOS without having a GPU connected.

I had a similar problem once, turned out my soundcard didn't really fit with my casing, so if I screwed it to my case, it would be plugged slightly out of the motherboard. Result: didn't boot!

You are correct when you assume the PS, MB, & CPU. It could have been a power spike that killed it or just overheated or just old age. Since you don't have parts to swap, it's hard to go forward. If you get fans, the PS is probably good.

It looks like the MB/CPU might have died on you...

EDIT: Since there is no beeping and it is random, I believe that your CPU is failing on you. I had a similar situation recently. If you can replace the CPU, then you might be okay to keep using the same system.

-JFV

There are lots of things that would keep a system from always powering up. It would take an experienced engineer a few minutes to days to debug an issue you are describing. As mentioned in other Answers, it could be the GND, one of your add-in cards or modules or your motherboard components that have a problem.

Some other things that I can think of from my experience/perspective (although improper assembly and/or bad add-in cards and modules are much more likely to be the issue):

• A incorrect BIOS setting (try to update BIOS, clear the CMOS and use default or safe settings).
• DC-DC power supplies may have design issues which keep them from always powering up.
• The power up timing is out of whack or power sequencing control wasn't thoroughly validated.
• The actual important components on your motherboard may have an issue which had gone unnoticed or the component manufactuer made a "business" decision that the issue wouldn't affect anybody.
• Capacitors on your motherboard could have failed, maybe you can see the electrolytic cans casing bulging outward.
• AC silver box (ATX Power Supply) didn't reach it's minimum load so that it can power up. Some power supplies require a certain load on their different power rails before they will power on.

(I'll add more to this list if I think of any.)

Generally debugging a board requires taking it out of the chassis, getting a hold of the schematic and layout design files, and taking measurements with a meter and oscilloscope to determine the exact cause of the failure after the easy stuff is taken care of (testing with a known good configuration, clear cmos, etc.).

Might sound silly but.. are you sure that there's nothing making ground? I've had experiences of odd situations where the motherboard itself or a PCI card was grounding with the chasis and refusing to boot

Like others here, my gut instinct is pointing at the CPU.

I had a situation like this a few years back, and it turned out that the CPU and MB were both fine, but the cheap thermal paste connecting the heat-sink to the cpu had broken down to the point where it wasn't making a firm connection between the two anymore.

I was ready to replace the CPU, but on a whim I picked up a new tube of thermal paste for 5 bucks, applied it, and the machine has been running perfectly ever since.

Does it beep when it fails to boot? It could be failing to POST. If there's a beeping pattern, you can check your mobo manual (or website) for what the pattern of beeps might mean.

Hardware problems like this are very difficult to troubleshoot, but I have personally run into the exact symptoms you describe on a couple of machines and it turned out to be a bad power supply both times. In each instance, the fans spun up and the lights came on as you mentioned, but the machines would not POST / boot. The power supplies even tested OK according to a power supply tester tool, but both times, swapping in a known good power supply fixed the issue straightaway.

Points on similar lines at Computer wont POST after power outage

I had a problem like this once, turned out to be a motherboard problem. Replacing it fixed the thing right up.

First thing is first. ALWAYS check ur connections. Check the CPU power cable that goes into the motherboard is properly seated. Also I agree with RMONTAGUD...verify that nothing on the MB is contacting the chassis.