Things heat up and expand either toward a good connection or away from one.
Try a systematic approach, such as rule out a monitor and cable connection problem (try another monitor, cable, clean connectors). Then open the case and reseat chips; look here for loose cables.
While under "load" carefully check the PSU for voltages concentrating on the +5 and +12 as they are the most heavily burdened. Keep in mind that every Amiga "expert" hears of a problem and posts Capacitors and PSU. A2000's tend to not have the former, and every hoofbeat does not come from a Zebra.
