There are many USA proxy sites, but most of them don't really hide your IP address. To make sure that a proxy works and hides your computer IP address visit "whatismyipaddress.com" though a proxy server, once in you will see your present IP address and it should look something like this:
This is one of the many USA proxy!
IP Information: 199.217.117.144
ISP: Hosting Solutions International
Organization: Hosting Solutions International
Services: Network Sharing Device Recently report forum spam source.
City: Saint Louis
Region: Missouri
Country: United States
Now, I live in Spain so obviously my IP address has been changed! If the IP address shows as your real IP address then try another USA proxy.