pc shuts down randomly

Hi there

my computer shuts itself down randomly.  Sometimes after 3 seconds,
sometimes after one hour or sometimes not at all.

i have norton AV and PFW 2003, i have tested my computer for the blaster
virus.

the problem started when i moved to my studenthome at the University of
Louvain, Belgium.
the university offers broadband internet to everybody (a LAN).  Maybe there
got something in via that connection?  But I think that network is very well
protected.

Or could it be the change of enviroment?  Could it be the heat?  My pc is
between my wooden desk and a wooden cupboard, just on the carpet floor.

please help me, because i can't trust my computer anymore...

thanks
Jens Gabriels,
[EMAIL PROTECTED]

AMD XP 2.6
Fan Taisol for AMD Duron & XP 2600+
MB ASUS A7V8X-X (AMD XP & Duron) KT400 + Sound
DDR 512 Mb 333Mhz PC2700
Geforce 4 Mx440 64Mb + TV out
DVD 16x
CD-RW 52/24/52
Tower ATX 300W 4 BAIES
Floppy 1.44 Mb
HD 80Go 7200RPM