Epox 8K3AP

AMD 2000XP 512 meg ram 60 gig hd new installation of XP home
brand new everything.....
this board is exhibiting the following behaviour:

the power LED on the case is always on
[ unless the power cord is pulled]
when you press the start button
fans go on
cd rom lights flash
nothing on the post LED at all
hard disk led on
itsw stalled.......

press reset and it boots normally into win xp home
if you shut down and turn it on within a minute it starts straight up
if you wait around 5 minutes or so it repeats the behaviour described
in paragraph 2

what is it??.....i had this built by the supplier and i took it
back....they said it was a motherboard issue and that they replaced
the board

well i get it back here and you guessed it......exactly the same
problem....
any ideas gratefully received
ray