PC won't always start (motherboard).

About half a year ago my computer began to not always start. When I power it on, the fans will get power (they are directly connected to the PSU) and spin up.

When it does start, LED's on the motherboard light up - fans drop in rpm and the system boots.

When it does NOT start, LED's wont light up - fans stay at max rpm and screen keeps black.

Keep in mind that when the system is up and running, everything works perfectly.

It never crashes.
It performes like it should in demanding applications such as games etc.
Temperaturs on CPU and GPU are normal.

It should not be a problem with the PSU as I have had the problem with different PSU's.

One thing to note is that let's say I unplug the power to my additional HDD's the computer starts pretty much every time, but not always (9 out of 10 or something)

With both my HDD's connected is when it starts to become more like 50/50 if it's going to start or not.

I'm thinking there might be a problem with the motherboard, but I'm not sure since the system runs perfectly once it's up and running. If it was anything major I assume the system would either not boot at all or it would have alot of hardware related crashes.

It's a 750w PSU so the power isn't the problem.

A few things to check out. Check to make sure that all the hardware is fully seated in their respective slots. Make sure that all cabling is properly connected and fully seated. Then make sure that you have all the latest drivers for your mobo and hardware. This may include a BIOS update as well. With out any system specifications it's just a really hard to advise.

Motherboard: Asus Crosshair III Formula.
CPU: AMD Phenom II x4 965
RAM: 2x2 GB Corsair Dominator 1600MHz
Video: Asus GeForce GTX 275
HDD1: Samsung SpinPoint F3 HD502HJ 16MB 500GB
HDD2: Samsung SpinPoint 500GB (older SpinPoint, don't have all the info right now as it's not connected)

3x80mm and 1x120mm chassi fans (Connected to PSU via Molex)

Bios is flashed to newest version (had the problem before upgrade as well).

Like I said before, I've noticed that with only the first HDD connected the chances of the computer starting up are far greater then with both of them connected. Eventually it will start it's just that with the one HDD connected it might be 8 or 9 out of 10 times but with both of them connected it's more like 5 out of 10 tries. (It's rather random most of the time)

It should not be a problem with the PSU, I've had the system boot on only 450W PSU - and now I'm 750W - keep in mind that with the 750W PSU, once the system is up and running - it's dead stable.

One thing I might add as well is that a year or so back my old (5 year) 1250W PSU died on me, so I bought a new 650W PSU.. then that one died after 6 months (that one wasn't of the best quallity). While waiting for my new 650W I used only a 450W PSU for a month and then I got a 750W instead (which is the one I'm using now).

TVeblen said:

You could have some funky power issues coming from the motherboard side of things. It is unusual to have that many power supplies die in a row, regardless of quality.

Do you have a multmeter that you can test power levels with?

Yes I thought so to, however they most likely did have alot of dust in them just like the rest of the components. All blown out now however.

I do not have a multmeter, I could probably get my hands on one tho - Seems like there should be some problem with the motherboard doesn't it? At least thats the feeling i've had. Can't be that major of a damage tho, since the system runs dead stable once it's up.

Now that is interesting.

So disconnecting the fan brings up some more questions/possibilities:

• Could that 120 fan be defective (shorting out)? Did you suspect that fan for some reason?
  
  It's the biggest one and is most one and is most likely using the most power to spin up. Plus for cooling purpose, being a fan on top - it's the one I'm the least concerned about.
  
• Is there cause and effect? If you plug the fan back in does the problem return?
  
  The problem is to random to be sure, as you might remember alot of the time the computer starts on the first try, however today it didnt. The only thing I guess I could look at is the animated logo, if it goes back to stuttering/laging or not
  
• Is that fan connected to the motherboard? Is that where it gets power from (as opposed to a separate molex power connection)?
  
  It like all the chassi fan's are connected to the PSU.
  
• What happens if you plug that fan's 3 pin connector into a different fan header on the motherboard?
  
  Can't molex connectors only on fans.
  
• What happens if you reconnect that fan and disconnect another?
  
  Like I said above, problem is pretty random so.
  

The cooling fans use 12v power also, same as hard drives, CPU, & Video card. So this still leaves the 'poor power' issue on the table. But more experiments and tests could narrow down the cause.


One note: what you have done now is a workaround, not a solution. You will want to find a solution to avoid potential damage or creating a new mystery problem.

Yes, however I'm thinking whats the difference between having fans connected to mobo headers instead? Note that it's 4 fans set to max speed that needs to spin up first thing when the computer starts - this might not be optimal? How does the mobo controll this differently? Also I didn't have the problem with my old 1250W PSU before that died on my after 5 years of use. Then again, the problem could have started as it died.