controlling the computer case 'output' air.

My case with lots of goodies inside, like an AMD 1800+ and two 100+ gig harddrives and ram, and v-card, runs very smoothly. After about 12 hours of operation, my computer's fans output very hot air, and becomes very unstable, and loses video output "vga signal not detected"- says my monitor. Should i get another case with more case fans? Is this characteristic of an 'overheating' problem???
snuffleupagusnbigbird0@hotmail.com
Thanks.