Since you were messing with ROMs, I would check there are no pins crunched up, etc. Also make sure battery is not leaking or any traces ruined from past leakages! And SCSI termination! I have had "dead" A3000 symptoms, ie turn on and no power or lights with just a missing terminator! Yes it's true.
Also IMHO the A3000 is the BEST built Amiga. Just because yours is having a problem ~17 years after it was released does not mean it is a POS! I would like to see what your new PC or Mac does in 2024. :crazy: