I had a similar problem using a new production kickstart in an A500. There's a thread over on eab.abime.net that details a fix that worked for me. The fix is to install resistor packs that act as pull ups on the address bus. The board has pads for the resistors, but they weren't needed for the older roms, so they weren't populated from the factory.
Here's the link:
http://eab.abime.net/showpost.php?p=525862&postcount=322This one had a similar fix, but attaches to the rom socket rather than the motherboard:
http://eab.abime.net/showthread.php?t=82824Ack, I read gray but missed workbench! My symptoms were slightly different. My machine usually froze at a gray screen during the early boot, but occasionally made it far enough to boot from the floppy (before freezing at some later point). If yours reliably boots to workbench, this might be different.
In need of coffee,
Robert
