[Coco] CoCo 2 problem

[Chad H]

Ok, I just acquired a new CoCo 2 unit (26-3127B) of unknown condition.  The
unit looks immaculate inside and out, I had good hopes.  It did operate
great for about 5 minutes then started acting funny with disk access.  I
turned off the computer and rebooted and would either get garbage (columns
of funny text characters) or a good boot screen (Microware copyright
statement with "OK") but there is no flashing cursor.  Anyone ever see this
behavior before or know what it probably is?