Graphics card not performing properly?

Hardware GPU
1

Specs:

CPU: Intel core i5 3570k.
Motherboard: Gigabyte GA-Z77-DS3H Motherboard
Graphics Card: AMD Radeon 2GB Sapphire HD 7850
Power Supply: Corsair CX430
RAM: 2x4GB Corsair Vengeance DDR3
Hard drive: Seagate Barracuda 1TB 3.5″ 7200RPM
The rest isn't really important.

Anyway, people on YouTube are managing to play BF3, Skyrim and other games with relatively good settings and high FPS.

I'm struggling to hit 40 on Minecraft with fancy graphics.
Am I doing something wrong? Is there a part I need to improve my performance? My Motherboard is meant to use a 500w PSU but I'm only using a 430w, could this be the issue?
Any and all help is GREATLY appreciated.
Thanks.

2

Assume you are running the latest drivers?

3

That is a little bit low watts for your setup... but I doubt that's where your problem lies.  OC your GPU and CPU.  The videos you're watching are probably all using overclocked cards.  Also could be an out of date driver issue, as James said.