🚀 go-pugleaf

hi 
please help me diagnose this problem..............
picked up this machine and it was not posting....the hard disk lite
was locked on........i swapped out the hard disk initially and it
posted straight away...dead hard disk i thought.......so i ran it
overnight with diagnostics testing the hard disk to see if it would
blitz it befeore i bought a new one....next day it was still going ok
so i bought a new drive.....i ran xp setup and it formatted 33% of the
drive and it stalled.....i restarted the system and it didn't post
again....
Gigabyte &VT600-1394 mainboard / AMD XP2500 CPU / 512 MB DDR
there is no post.............when switching on, the hard disk LED
comes on the DVD CDRW combo  drive light flashes intermittantly and
there is a few weak pops from the speaker, [nothing that could be
interpreted as a beep code] the keyboard indicator is lit but there
are no flashes as per the normal boot sequence...... and that is
all...psu/cpu fans are spinning and the ram led is lit.....PSU
voltages are all reading correct levels....the motherboard is on an
antistatic bed with a 3rd hard drive connected to the power only, [the
hard disk is spinning ok], a pci video card and keyboard.......the
minimum config possible.... i have also swapped out the ram, video
card and PSU with no improvement.......it is down to the mobo or cpu i
guess unless i have missed something
thanks for any input