Blue Screen of Death........?

I/My Friend Purchased a New PC 1 1/2 months back
Its config is
Intel P4 3.4HT, 102DC Intel Board, 1GB Kingston RAM, 160GB Seagate HDD, LCD Monitor
He is getting BSOD (Blue Screen of Death)............
I cant understand what the Problem

actually today morning
the PC was not starting
CPU Light was their
but no signal was in the monitor
so I just removed the HDD cable & reattached it
now the PC started, WinXP screen appeared
&
PC restarted
after many attempt
PC on sucessfully

now it was restarting in between (approx in 10 min)
so I disabled automatic restart from Mycomputers > Properties
Now i am getting BSOD

Pls can someone tell me how to identify whats the prob

he also has one old PC
with config
Intel P4 2.8, 865 Intel Board, 1GB Kingston RAM, 80GB Seagate HDD, 17" Flat Monitor

it is also getting the same BSOD error

Pls help.....................