Open Google, set it as the default homepage. If you want a more specific instructions then you need to provide more information, like the browser you are using, and what changed the homepage in the first place - if it is an infection of some sort then just changing the homepage back won't work.
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd
If your homepage suddenly changed without you doing something then this is most likely due to a virus. We need more information. Always pop back and let us know the outcome - thanks
