Harddisk problem

Hi!
This is an unusual problem.
My PC configuration is: Duron 750MHz,256MB SDRAM, MB Matsonic 8137+(KT266A),
and I have 2 harddisks, both of them Maxtor:one is 80GB(primary) and the ot
her is 15GB(secondary).
The problem is that I can’t work under Linux anymore. If I try to install so
mething which overstresses(for example Sun Java Studion Creator), it begins
to install but after some minutes of “hard work” everything blocks. I reset
the PC and BIOS can’t find my primary HDD(even with autodetection).
If I don’t do “hard work” under Linux (just browsing and listening to music)
, there is no problem, only when the HDD is overstressed.
After this, I shutdown the PC and everything works.
I must mention that I don’t have such problems under Windows(2K,XP), only under Linux (Slackware 9,10, RedHat 8).
Thanks.