Is it still switched on or have you powered down and re-booted? This happened to me a couple of days ago following a windows update - powering down and re-booting fortunately cleared it for me.
You say that the start button is there - did you click on it to see if it opened? Is there a dvd or cd in the drive?
It could be do to the video driver needing updating.
It may be for some reason that the resolution of the screen has been altered.
If you can get into the control panel after clicking on the start button, then go onto display, settings, and check that the resolution is correct for the laptop display.
Have a look at this article explaining how to do this.
To start in safe mode you keep tapping the F8 button until the screen appears.