Many connections to chips and cards will go bad in an old amiga. If you are handy with tools, here's a list of things to do first....
Disconnect power and all other external cables.
Open the case.
Pull all extra cards from the expansion slots.
Remove the drive bays, power supply and the brace they rested on.
You should be able to see most of the MB now.
Take a look at this picture from AmigaU.com...
A2000 Rev 4.x MotherboardYour board may look a little different but should be close to this one. Press down on any chips that are in chip sockets. Don't kill it, but mash them well. It may make some crackly noises, that's ok. Also press on each of the four sides of the Agnus chip. Agnus is the big square chip in the right middle of the picture. (The chip is missing in this picture). Next take a close look at the battery (Blue battery located at the bottom center of this picture). On old systems this battery leaks and starts to eat the mother board. If yours has leaked, I recommend removing it. I have removed many a bad battery by moving the battery back and forth slowly many times until it breaks free. You can also remove the old one and put in a new one if you have the solder tools to do it with. The battery is not essential, but keeps the system clock when power is off. You will have to set your time when you boot up if you want the clock to be acurate.
After all these things are done, reassemble your drive bays and cables,
reconnect your power, keyboard/mouse, cross your fingers and turn it on.
Hopefully it will spring back to life. Let me know if it doesn't.
We can go to step two in maintenance....
Step 3 is to get it to a really good Amiga tech or buy another :-)
If it does come back to life, go ahead and replace the other expansion cards. If all is still well with all cards back in, you are rolling.
Plaz