@Pastor:
One flash with the keyboard led only, indicates that everything is fine with the keyboard.
If I were you I would remove as much of the expansions as possible. Try running it with only the 030-card, only chipmem, no Zorro-cards, no harddrive, just the floppy.
Just remember that it will take atleast 20 seconds if no harddrive is attached until it shows the bootscreen.
(edit): If the Kickstart ROMs are faulty it should flash a red screen when you start it.
Check
this link for information about what the Amiga do when you power it up. NOTE that the ROM in the keyboard has a checksum error only if the caps-led stays lit for several seconds, not if it flashes briefly once, that is perfectly normal.
(edit2): The A4000 motherboard should be fastened firmly to the metal base of the tower with screws in every hole as it uses the screwholes, screws and the chassis to make its groundplane complete afaik.
Good luck!
/Patrik
