Computer doesn't turn on normally.

[MTG2008]

I've had my PC for about a year and a half now, and up to now the problems have been minimal to non-existent.
Recently however (last week or so) my PC won't turn on via the front power on button, without switching the actual power supply switch off then on.
It will usually turn the leds/fans/components on etc. for less then half a second and then a few seconds later do it again but they'll be no front power light.
Also unplugging it and plugging it back in, switching it off at the mains etc. doesn't help. It only usually works when I use the actual power supply switch to click on/off.

The power supply in question is SuperFlower Leadex GOLD 650W, and with the recommendations I had for it, as well as the gold rating, I'd hate to think it was the PSU, however it seems pretty evident at this point... I know the motherboard could also be an issue but not too sure on the specific procedures to diagnose and troubleshoot.
So could anyone give me a small guide on diagnosing/finding the problem, or whether or not they know if it's the PSU for sure.

Thanks

 

[MTG2008]

When my old pc wouldn't boot it was a weak 5VSB rail on the psu - it did the same starting to boot that yours does, then stop, then the fans would just come on or it would just fail completely.
I found unplugging USB devices could help get it to boot but it was pretty hit and miss

You can test it with a multimeter across the 24 pin socket

I thought it might be a USB problem at first because sometimes my mouse would lag a little and my keyboard sometimes malfunctions (ghosting randomly) so i thought if enough power wasn't getting to them, maybe it's too much load. I have 2 hard drives (externally powered), an audio interface and keyboard/mouse (both have LEDs in them) to power.
Turned it off and just unplugged everything and no luck again. It seems I have to cycle through turning it off from the mains and the actual PSU to get it to switch back on.

Not got a multimeter so might get one if that's the best way of testing. I assume I'm looking for around 5v on the socket when the PSU is switch on the mains but off then? From what I understand you're saying is, if the rail is weak and not holding/getting the 5V when the mains power is connected then the motherboard can't tell the computer to power up, or just not getting enough power to power on? (I have very little electronic knowledge!)
In theory, this sounds like a very plausible explanation for my problem though so thanks!

 

[MTG2008]

Having similar issues with my PSU I suspect. Any update on how this went for you?

Still busted :/ went away for a few days and came back, it turned on straight away... Then after that it takes between a minute, up to about 5 minutes to turn on. I might just email the manufacturer...