Okay guys. I've been thinking of buying a MSI Radeon 7770 1 GB to replace my crappy Sapphire 4670 HD 1 GB. My power supply is 400 W. Is it enough for the 7770? And do I need an external power supply? How do I get that? What is a 6 pin connector? Do I have to buy a new PSU? I really need help.