laptop is not starting up, only LED blinking once. Pavilion

[peer1]

HP pvavilion DV 9812us

When I try to start up my laptop:

The LED lights above the keyboard light up for one second, there is a slight noise during half a second. The everything stops

The Hard drive is checked by me, the RAM I pulled out enput back again

[Scolton]

This may sound stupid, but, is the battery dead? This is common reaction to a dead battery.

[peer1]

Thanks for your reaction.

No, the battery is not dead. The same symptoms are there if I connect the laptop to the charger.

There are not lighting Led's next to Capslock and Page up.

The laptop is from 2008.

I wonder if the motherboard is broken, but I do not know the signs of this catastrophe.

[Scolton]

I DO know signs of a dead motherboard, because I once told a neighbor that their laptop had a broken motherboard, and they took it to a Best Buy, who took the exact same steps I did and they recieved the same response.  I believe that this is a shot motherboard, but I just wanted to get the battery thing out of the way first.  You may want to consider a new laptop, as this is not an easy fix...

[peer1]

Thanks for your reply,

so what are the signs of a "shot" motherboard? 

i saw some you-tube movies on repairing a motherboard with heat: to repair the connections. I do not know how succcesfull they are. My laptop was a pretty expensive laptop IMO, so I do not want to give up immediately and try to  solve the problem without buying a new one.

[Scolton]

I guess for a shot motherboard, you will find that LEDs function, but you will never see signs of an operating system startup. It will also seem as though the video card is broken
I can come up with more but I am really tired today so I will get back to you with more info.

[peer1]

Additional information,

exept of the small , less than a second lasting noise, not being a beep, there is no noise of a turning HDD. 

Neither is there any light nor a flash, nor a stripe, not to mention a letter or number on the screen. It remains blacker than the universe.

Sleep well.

[Scolton]

Have you checked the power supply?

[peer1]

When I connect the power supply to the laptop, there appears a blue light at the side where the connector fits in the laptop.

Also a blue light appears at the front side of the laptop, which means the power is on. So I suppose the power supply is working.

 I did not disasseble the power suply though, to check alll the connections inside with a multimeter.

[Scolton]

You just went way over my head. I have no idea what a multimeter is. I still have to say that you will just want to order new motherboard. It will fix your problem.