When Ubuntu Linux is loaded on many laptops, the sound does not work initially. This is true for the Gateway MX7118. So what's up? Well, it's pretty simple. Linux is sending the sound to an external speaker. The problem is that you don't have an external speaker. So here is how to fix the issue.
1) Double click on the speaker icon in the System Tray to bring up the mixer.
2) Go into preferences and make sure that "External Amplifier" is selected to show on the mixer.
3) When you go back to the mixer, you will have a new tab "Switches." Select that tab.
4) Uncheck the only box on that tab. It's the box marked external amplifier.
5) Close mixer. Your sound will now work!
For more info, go to ubuntuforums.com