• Outlets: Start at the wall. Is your outlet active? Is your power bar turned on? Sometimes it can be as simple as the cat walking over a switch, so start there and clean those dust bunnies while you're down there!
• Cables: It's easy to shift something or kknock something loose, especially if you unplug and replug a laptop. Make sure all your cables are snug and secure.
• Virus Scanner: Sometimes after a particularly nasty virus or bug has been deleted it can play tricks on your system. Try going back in your history logs to do a reboot from before you ran the scan. Even if you haven't done so before, most systems have this built into it.
• Fan: After opening up your computer and blowing out all the dust that has settled into place, make sure your fan is in fact working. If your computer is overheating, several things are known to shut down to avoid further complications and it can all start with the fan.
• Different Mode: Try starting up in Single User Mode for Macs and Safe mode for Windows. You should be able to eliminate some issues or hone in on the problem if either of these work for you when your computer wouldn't boot before.
What are some of the first things you try when your computer gives you the proverbial finger? Share your tips and tricks in the comments below!