Ok
Just before you kick up an almighty dust storm and never return back from it can I suggest you avoid doing too much. Very often it is a simple thing that is at fault. I have checked over your motherboard and it looks exactly the same as mine.. except mine has a Treops RAM Board with an external switch.
The metal clamp over the Agnus is normal so don't worry about that. For me I never remove motherboards from their casing unless they are busted. Especially on older kit. Sadly in replacing the floppy you unsettled something. That is assuming you didn't remove anything else. Don't remove anything else.
First up check the power supply and I mean the connector on the back of the computer.
Then check any other ports you have plugged in. And have you other cables and connectors you can try.
Check the machine with the keyboard lifted up and the shielding also lifted up. Be careful and don't touch anything.
Check the power connectors to the floppy drive and the ribbon connector to the floppy drive.
Gently press all the chips to make sure they are seated properly.
By removing stuff you are at risk of kicking up a dust storm and unless you are elctronically skilled and can check circuits you will never find your problem. Nine times out of ten its just an electrical short or poor connection.
I just had a yellow screen on a 500 and decided to go in and have a look. Seriously, all I did was lift the shielding and depress the main CPU and ROM chips and she booted no problem. Still running now. The trick is to avoid doing too much. You may think you are doing right by cleaning but in truth you are likely to generate even more issues. The trick with old kit is to get it running and keep checking but don't keep unplugging, moving about, opening up, disconnecting stuff. That may have been OK when the kit was new but in an aged state unless you are skilled at mending electronics or can afford to ship to someone who can, then leave well alone.
So small steps is what I would suggest.
I asked for the SERIAL NO. Would be useful.
