Display Resolution (screen size issues)

I am having issues with adjusting my screen size to the full stretched size, it has reverted back to a small box size and will not stretch out at the sides to fill the full size of the screen anymore. I have tried to adjust it back in System Preferences > Displays but it does not bring up the same size resolution that I used to use anymore which is very strange. This is quite annoying if anyone can help or shed any light I would appreciate. Also the other thing that happened was that I had to restart my computer and my homepage on Safari had been changed to Apple.com instead of Google.com which was what it was set at. This occured at the same time my screen size shrunk. Thank you