Old Precision T5500 No POST

Did you try replacing the size 2032 MB battery?  Bad batteries affect BIOS and therefore PC operation.

Yes, I insured there was a new battery and checked it with a DVM. This is a really weird issue as the CPU is not powering up which I verify as in not heating up. Power connection to cpu1 has each of the 12vdc levels on it. Power supply tests good. Tried different DIMMS, two different GPUs. I bread-boarded it and still nothing although doing that prevents the led code panel being there. I’m at work this moment so I can’t do anything till later today. In bread-boarding it, I did not plug in the cpu cooling fan so I’m wondering if the MB has a built in protection to not turn on if the fan isn’t present. In the chassis, of course the fan was plugged in properly and operating. Still didn’t work initially. 

Also, did the reset BIOS using the included jumper as told in the manual which had no effect. 

For anyone following this thread, I've connected the fans which made no difference. I did pull and connect the chassis front panel led display to the MB. Still just get the solid green from the power on button and nothing else. The MB is not powering up although the chipset fans, cpu fans, psu are all powering up. I'm starting to wonder if the MB BIOS firmware got somehow erased. I've got the newest A18 firmware update on a flash drive ready to go but it doesn't run so no way to update the BIOS. I've ordered a psu diagnostic device which will come in two days. I have no way to test the PS ON function which is a millisecond output but this device will do it. So unless I've got fried CPU's, fried DIMMs, Fried GPUs...everything else is disconnected. I don't even get the hardware beep codes.

Sounds like MB may be defective and/or bricked itself.  BIOS/CMOS may have become corrupted.

I take it that it doesn't allow you to get to F2 BIOS or F12 Boot and Diagnostics menu.  If it allowed you to get to the aforementioned menu, you could run diagnostics.

I get nothing on the screen. The cpu doesn’t warm up. I wish I could get to the diagnostics. 

I’m wondering if Dell would be willing to share the full schematic of this MB? It’s an older machine and I fully understand the copyright issues but I’d like to resolve this issue. I’ve ordered another one off eBay but I’d like to understand what’s wrong with this one. 

Dell has never released full schematics. The online Precision T5500 Documentation page list all that we released.

Thank you Chris. I’m guessing for the cost to have Dell actually look at this machine, I could literally purchase a state of the art new machine. It’s been long out of warranty forever. 

"I’ve ordered another one off eBay but I’d like to understand what’s wrong with this one."  Ordered a new PC or MB?  Used/refurb MB's on eBay aren't too bad on price.  Some sellers are ridiculous though with high prices.

Probably wouldn't take much more to have a newer PC.