Dimension E310 won't turn on - solid amber power light and 1 2 3 4 diagnostic lights on

Hello,

I have a 2 year old Dimension E310 that won't power on.  The power light is solid amber, and all four diagnostic lights are on when I try to turn on the machine.  Unfortunately the warranty has expired last year, so I tried to troubleshoot the issue on my own, though without any success. 

I have tried swapping in a new power supply, a new CMOS battery, reseated the processor, reseated RAM dimms, and reconnected all connections to the motherboard.  Still no luck.  My final guess is that it's either the processor or the motherboard.  Any help with this issue would be greatly appreciated.