65c is not hot for a graphics card.When it hits around 80c then id start worrying.As for your pc shutting down could be psu not giving enough power.Give specs and how old the comp is. Could just need a good cleaning.
i have intel Core2duo 2.4
4gb DDR2 Ram
Native 450W PSU...
GTS250 512mb DDR3 256bit..
but don't how to check how much voltage GPU is Using...