Try it without the Voodoo card, The Voodoo drivers are known to be unstable in many cases (Not mach related, just in general). If you have any other video cards laying around that would be were I would start.
Hard restarts without the bluescreen of death are almost always hardware or hardware driver related.
Other thing to do to narrow down the the problem: Right Click My Computer, Properties, Advanced, Under Startup and Recovery click settings, then uncheck Automatically restart. This way if it is a windows related problem you will be able to see/read the error messages so we can debug further.