"New" A4000 power problem

[stopthegop]

Hello
Just got a "new" A4000 desktop off craigslist.  It was advertised as non-working, good for parts only.  Paid a whopping $30.  The machine is actually complete and in decent physical condition incredibly, with no battery leakage.  It has a power problem though and I just wanted to fish for ideas here before I get too far on the wrong tangent.  It powers up for maybe three seconds, then just shuts down.  The fans spin, but not as fast as you would think.  When it gets power it sounds very "weak", then just shuts itself off.  The PSU is ok, I think.  5v and 12v output are ok.  115vac input is good, too.  Its got a 3640 installed and thats it.  Any suggestions?

[stopthegop]

I don't think it the power supply.  I swapped with a known good PSU.  Same problem.  Well, not exactly.  Now I get a bright green display before it shuts itself off.  Previously it just shut itself off after 3 seconds.  Now it stays on for perhaps 10 seconds, displaying bright green from the AGA port immediately before shutting itself down.  Bad memory?  Zorro problem?  AGA problem?  What would cause it to just lose power like that besides the PSU?