Default Gateway Not Available (Have Nvidia graphics card)

Hello, I got a PC from a buddy of mine for Christmas and when I wiped it and reinstalled Windows 7 64bit, I now cannot download anything large, watch youtube videos, and online gaming cuts out. I have an i-5 processor, 4 gbs of RAM, and an Nvidia GeForce GTS 250 as my video card. I'm using a Netgear WNA3100 N300 Wireless USB Adapter and whenever I try to download anything I receive an error,...