weir crashes :-/

hello everyone,
some 3d functions seem to make my machine crash,(i am working on windows98 with 2 graphiccards: primary: nvidia tnt2/ 2ndary: s3 virge (deactivated actually)).
the crashes happen in a weird manner: first the monitor goes black, some seconds later the computer reboots, it seems like the graphicCard crashes first (possible?).
i already installed several drivers to get rid of this problem (glSetup, newest directX)
= no success.
anyone having an idea what might be the problem / how to solve it?

thx in advance