I would take off the top lid of the computer
 and try to pinpoint where exactly the heat is
 coming from.  There could be some components
 that might have shorted out and is causing
 the power supply to output more current.  This 
    Oh, the "loved" a600...
    These have a very common fault - Capacitors. They leak and play havoc on
your system. Dunno where you live, but in Brazil it is very very very
common. People sez it is because of the (high) temperatures around. But I'm
90% sure your problem has to do with caps.
    I'd suggest you another A600 or a 1200 if you can get one (I had a 600
and now have a 1200, love that puter!!!). Take a look at the "amigo" on
www.tabajara-labs.com.br :oD
    See ya
    Alexandre Souza