Inspiron 530 desktop problem

Hello gang, I am in need of advice and or help.  I have a Inspiron 530 desktop with recently developed the constant amber power light and will not turn on.  I can disconnect all power and let it sit over night then reattach the power and it will generally power back on.  However, it will always boot to the message screen which states it was not shut down properly and prompts you to select how to boot.  I.E. normal mode, safe mode, ect.... Once selecting normal it boots up. 

There has been several times lately it hasn't wanted to come out of the amber no boot mode.  Here is what I have done so far.  I disconnected all of the peripherals to see if it would boot to a raw dos screen. It did not.  I still maintained the amber no boot power light.  I then decided while everything was disconnected, I would also disconnect the two brown two, black processor connector.  It powered right up.  But obviously without the processor power all it did was run the fans.  Now, while it was on and just running the fans I carefully reattached the processor power connector and it booted to the dos prompt stating no hd present.  So then I shut down, reconnected all the peripherals and once rebooting same thing, amber light.  I disconnected the power and once again removed the processor power connector.  Rebooted and again, straight to green light.  I again reconnected the processor connector while it was powered up green and it booted right up. 

While it was up and running I went to the dell online diagnostics and ran a scan.  It stated both motherboard and processor were fine.  However, it found problems with the hard drive.  I find that hard to believe because I will still have the amber light issue even when the HD isn't connected.  So I am trying to figure out if there are any other tests I can do to determine whether it is the motherboard or processor causing this problem.  My hunch feeling is it a a motherboard issue, but I want to be fairly certain before I replace it.  Any thoughts would be greatly appreciated.   

Semper Fi