i never had a problem with WC3 using my geforce2 but that happened to me too when i used a radeon 7200, you can give different drivers a try - try one that is WHQL certified for geforce4, and tweaking the settings
Are you using windows xp? If so, try to generate a BSOD (Blue Screen) error (instead of automatic restarts) it will be helpful because then we can use the information in it to figure out whats wrong. To enable the computer to report this error instead of just automatically restart or freeze try this...
Right-click my computer
Startup and Recovery Settings
Uncheck automatically restart and make sure everything else Under System failure is checked
Also check the event viewer, some information might be in there, too. If you do get a BSOD copy down what it says. Thats very helpful in solving problems. Good luck! Let me know what you find out.