Baby steps to make your B2000 comes back to life.
1. Open it and gently pry the ROM out and them put it back to its socket;
2. Do the very same in any other socketed chip you see;
3. Remove the battery! Those evil batteries have killed a lot of good Amiga hardware around the world. I you mind the lack of a clock source, use a "lithium hack" (put a socketed coin shape battery with a germanium diode to avoid the recharging system to blow the battery);
4. Check the caps in the PSU. They may have dried, bulk or (worse) leak inside the PSU, destroying it. Those electrolytic caps are inexpensive to buy and easy to swap.
