I often wonder if anyone actually reads these posts before offering advice!
Since a stock A1000 has NO ROMs, this can't be the trouble. The 256Kb front RAM expansion could have a corrosion issue where it plugs in - this will cause problems. Also check for corrosion at every plug in the computer, and clean well.
Also a good idea to check PSU's output with a good multimeter.
If it worked OK when it was put away, it should be close to working...
