Nope, this is the zero crossing detector circuit and has no effect on the CPU accessing the ROM at U6 to boot.

This is a symptom, not a cause of the board not booting.

Have you carefully checked your solder work around the IC sockets to see if there's any accidental shorts between pins/traces?

Can you post some high resolution clear pictures front and back of the board?

Hmm, the lighting is not well enough to see clear fine detail in the pictures. Any chance you can take the photos outside during the day (but not in direct sunlight) and possibly higher resolution?

I can't quite tell but is there a short circuit circled below?
MPU100_ita.jpg

Where possible, check the IC sockets you've installed using a light from behind the board to see if you have any short circuits front side of the board between the pins and traces between them under the sockets.

MPU_Sockets 004a.jpg

Thanks, these pictures are better.

The only thing I can notice is it looks like you have bad corrosion under the J5 pin header that could be causing resistive shorts. Carefully inspect it and if it is corrosion, remove the J5 pin header to clean it.

BTW since it looks like there is corrosion at the top of the board, what condition is the CPU socket in?

Understood - we didn't question it