My Computer Doesn't Start

Yesterday I was using my laptop as normal and suddenly the internet disconnected, and then refused to reconnect. I tried to troubleshoot in Network and Sharing Centre but nothing came up, so I restarted to see if this helped. After restarting the internet still wasn't working (I have a wireless connection) so I thought the problem may have been due to a system update that was installed that morning, so I did a system restore to that point. However, upon restarting, the computer stopped on a black screen.I then turned the laptop off at the switch and back on again, however the computer got to the stage that the log-in screen should come up and remained black. Now, whenever I try to turn the computer on, it gets to just before the log-in screen and remains black (however the mouse remains on screen and can be moved) - also, Safe Mode doesn't start either and stops at a black screen shortly after I choose to start it.