I have 2 RPis, both version 3, model B. One has V 2.1, 2015 stamped on it, the other has no version, just 2017. I have 3 SD cards; the 2015 PI boots with the two that I had before recently getting a new PI- the 2017 one. This 2017 one, however, will no boot with either of the earlier SD cards, only with a pre-loaded Raspbian O/S SD card that came with it. With the other two SDs on the new RPi (Android, and another Raspbian install) I get the underpower lightning icon with the rainbow screen and nothing else, no green LED light. Inserting the new SD into the old RPi, I get plenty of green LED activity but the screen stays whitely-blank.
I am using an HDMI Waveshare screen for both RPIs.
That power may be an issue is perhaps reinforced by the fact that the 2017 RPI only works with two power cables, one for screen the other for the PI - with only one cable the boot process gets so far then restarts, over and over. The 2015 PI works on one cable.
I have tried using the config.txt file from the 2017 pre-install SD on the other Raspbian SD but that did not help. I would be grateful for any other ideas.