How do you start a crashed computer?

It depends on what operating system you are using. On most Windows operating systems you can get into what is called safe mode right after you reboot. You do this by usually pressing F-8 over and over as soon as you start your computer. I have seen it F-10 as well. Safe mode will often allow you to get the computer up and running with minimum drivers so you can reinstall or uninstall a program that is causing the problem, run scan-disk or some other utility. If you know what you did just before it crashed you may be able to undo it such as change some settings under control panel.

Downloading new drivers can solve some problems if you have an idea what device is causing the problem.

If none of this works you can always try and save stuff to a thump drive or something and then reinstall Windows or even format your hard drive and reinstall everything, though that would be a last resort.

If the problem is hardware it will have to be replaced.

If all else fails you may have to take it to somebody to get it fixed.

If that fails you can always take out your aggressions with a hammer or toss the blasted thing out the window!!