Rendering Problems On Sony Vegas

Im trying to render a video I made. It is about 8 and a half minutes with hd clips and im trying to render it into 720p. Im not a pro with sony vegas and i have only uploaded maybe like 5 videos. It keeps saying low memory and keeps shutting down or canceling. I have tried closing all programs other then vegas and still, infact it was worse the second time when I had everything closed compared to having everything open the first time. Im going to try to restart my computer and try again but if anyone knows what i can do to make it use the memory better(ram i suppose) any suggestions would be useful.