Hi, The A2000 is the only Amiga I ever sold, and I've regretted it since!
After checking memory other things to check are weather any chips are getting too hot, if any push-in type chips arn't seated right, any corrosion on connectors (you can get connection cleaner in a spray can from electronics stores), and finally inspect for dry joints! Any A2000 is getting old, and areas that go through a hot-cold cycle are prone to this problem (basically the solder joints come 'unstuck' and need re-soldering, sometimes they also pull a bit of the circuitboard track up with them too).
Remember to earth yourself before touching stuff inside the case (by touching any bare-metal part of the chassis with the mains plugged in), and if you're not used to soldering get an expert to do it! One nice thing about the A2000 is it's much easier to fix physical faults than later models!
