HP a1730n possible motherboard failure

[PaulHikes2]

Hi - Problem with my HP a1730n.  Machine is 4.5 years old and all I've ever done to it was add a wireless NIC when new. 

Currently when I turn it on, all that happens is the fans (power supply and I assume the heat sink) come on.  Absolutely nothing on the display, keyboard light doesn't come on.  There is no flicker then failure of either: they stay completely dark.  The power light on the front of the case stays on, the processer light comes on for a split second when I first press the power buttonthe card reader light comes on, and the DVD drive opens and closes, but that appears to be it.

When the problem first happened, I thouroughly cleaned out all of the dust, and it restarted once, but the problem resumed.  Subsequent cleanings and blowing out the case allowed it to boot up a couple more times, but now is exactly as described in the first paragraph.  I tried replacing the power supply with a brand new one with the same specs as the original.  The large connector was a bit smaller then the original, but it attached using two less pins, and I got the same issue, so I returned the power supply.   

Does anyone have advice on next troubleshooting steps?  Remember, there is no indication of power on either the keyboard or the monitor at any point, not even a flicker upon pressing the power button.  Even though both power supplys are "known good", would it be worth my while to try a beefier one?  And what's up with the long connector on the new power supply being a bit shorter then the connector on the motherboard?

Thanks in advance for your help!  BTW, I did attempt to search for this issue in the other posts, but I didn't see the exact issue reported.

[Big_Dave]

Hi,

What large connector has two less pins?    Review this guide on Power supply connectors.