hp elitebook 820 g1 won't start power light flashes 3 times

[macscotia]

I have an Elite book 820g1, product id J7A41AW#ABA, which will not boot up. When I press the power on button, there is a brief light in the CapsLock key and power light on front panel changes from white to amber and blinks 3 times.
Before this started, I had been trying to refurbish/renew the pc. It came with a regular SATA hard drive plus a small solid state hard drive on a card located just above and to the left of the memory slots. The notebook had been running previously on Windows 7 but I wanted to do a clean install of Windows 10 professional.  The install formatted the SATA hard drive but windows install would not install on that hard drive until I removed the solid state drive and removed the raid setting in the bios. Windows then installed and the pc was running fine for the next few days. I left it for about a week and when I tried to use it again I get this problem with not booting up.
I've checked various HP websites and downloaded the latest bios. I did the bios install to usb drive and inserted in a USB drive on the 820g1 and followed the instructions - power on holding down Windows and B keys.   However, I get the same results - light on caps lock briefly, white power on then amber and flashes 3 times.

I've downloaded the 820 service manual and done a lot of searches but I can't find anything specific to this model to explain what the 3 flashes mean or how to fix the problem.
Is there any way I can get the pc working again?

[macscotia]

It would be really appreciated if anyone could even give some thoughts or advice on where to look for information on this problem.  I tried downloading the correct service manual but couldn't find any mention of a separate SSD drive, raid, or even any explanation or discussion of beep "lights" or bios options.  I googled these issues as well and keep finding info related to other similar models which may or not apply to my model.  That info often has different answers - different beep sequences, different meanings etc.  Really confusing.

If anyone has had a bios issue with this model or similar models, I'd appreciate your input and thoughts.

I've spent a lot of time  and work and some money on this pc over the past month.  As I said above, the HP documentation has had very little information on most of what I've encountered.  Very frustrating.

I've seem some HP people post on these forums and would appreciated their thoughts and suggestions.  

Hopefully someone will know something.