How to change from google.xx to google.com?

When I type www.google.com to use Google to perform a search, it automatically changes to www.google.es. This happened to me in other computers so I know that if I click "google.com in English" it goes to www.google.com. But with my laptop it immediately goes back to www.google.es and if I perform a search, it gives the results in Spanish first. Searching for pictures or news is even more painful. Could anybody tell me how to change the settings so I can use www.google.com instead of www.google.es? 

Solution

I did the following with Firefox and worked from three different countries:

• 1- Set Firefox's Home Page to http://74.125.127.100/

For example, Tools --- > Options --- > in the Home Page blank paste (http://74.125.127.100/)

• 2- In the top right corner of Firefox where the different search engines bar,
  • Click on the little down arrow, then choose Manage Search Engines.
  • It will open up for you a new window.
  • At the bottom of this window, click on "Get more search engines".
• It will open for you a add-ons page, write in the search box "Google" to narrow the adds-on.
  • Then scroll down to an add-on called "English language-specific Google search".
  • Click on Download now and your are done!