1St of all : check the psu !!!!
A "+5v" giving you less than +4.88v will give you random problems...
if you have an A600/A1200, then try to power it by the Floppy connector with an AT or ATX psu (take HIGH care of the connector sense !!!!!!!!).
SMD Caps in these machine start to fail nowadays !!!
Even a +4.98v by the "normal" PSU connector only give +4.76v when it's arrive on the Floppy connector !! So guess how much arrive on the cpu and ram ...
So power it directly by there, but take care with the connector position !!!!!!!!
