That's OK - I2C communication between processor and Si5351A is a whole other topic.
Good news is that your processor is alive and clocking. It is just having trouble
waking up the Si5351A.
What to do?
It is possible that they're out-of sync. Don't know why that should happen, but a reset
to the processor might jog it so they're dancing to the same beat.
So power up, and get your blank display.
Then momentarily short the "RESET" line to "GND" on the 6-pin "Prog Header".
Also called "ISP" header.
It sits directly below the power connector where +12V comes in.
Top left pin gets shorted to top right pin, just for a quick moment.
That reset might get you past the power-up transactions, and into working mode.
Something to try before replacing the processor.