My computer is becoming inactive when I try
any network operation.
The screen turns black and hard drive spins off.
When I move my mouse it becomes active for a while,
and then deactivated again.
I installed a server package of latest RedHat 9.0.
If it's Linux, you may have the APMD, Advanced Power Management Daemon poorly configured.
Try to use the "man apmd" command to get some of the options available to you.
You may also want to shut it off completely just to help isolate the problem better.
# /etc/init.d/apmd stop
# chkconfig apmd off
# /etc/init.d/apmd start
# chkconfig apmd on
It may also be some poor power saving settings in your BIOS. Check that too to make sure all is OK.