It's a good line from the IT Crowd on TV, but its amazing how often it works! If your PC or laptop starts up and then stops at a black screen, try this. With the computer on, hold the power button in for about 9 or 10 seconds (not less) until the computer goes off completely and leave it for a few minutes. In the case of a laptop, disconnect the power lead, turn it over and remove the battery pack as well. Then start it it up as normal. We call this a 'hard reset'. This also fixes a glitch with Windows 10 where the start button or Live Mail don't work.