Since I have been giving this answer to what seems to be the majority of recent, apparently diverse, problems with W8, I'll put it here in a sticky thread, so that I can at least post a link to it rather than continually repeat the advice in thread after thread. Windows 8 and 8.1 will install by default, and hence will come pre-installed too, with "fast boot" enabled in the Power options. That sounds like a jolly good idea, and if you continue to use W8 as a single OS on your PC you will no doubt think it a thoroughly good thing and mentally congratulate Microsoft for their wonderful work on speeding up the boot process, http://blogs.msdn.com/b/b8/archive/2011/09/08/delivering-fast-boot-times-in-windows-8.aspx especially if you've invested in a brand new UEFI PC and the POST/BIOS section of startup is similarly boosted. However, the fact that you are reading this would suggest that you are a multi-booter, one of that special breed for whom one OS is just not enough. The fact is that W8 fast boot just does not sit well in the midst of a multi-boot. If you are a W8 user 99% of the time and you completely understand what's happening when you "shut down" and "reboot" your PC, you can probably make good use of "fast boot", live with its advantages and avoid its pitfalls, but you are here reading this post, so the preceding part of this sentence probably doesn't apply. The problem is that "fast boot" is "fast" because it isn't a "boot" When you instruct W8 to "shut down" it goes through the pretense of doing what you requested, but in reality it secretly enters a hibernated state. When you next turn your PC on, it again pretends to boot, even giving you a boot menu, but if you carry on using W8, what happens is a resume from the hibernation masquerading as a normal boot, hence the rapidity of reacquiring your start screen. The first indication you get of what is going on (if you hadn't already read the above MS blog) comes when you decide in the "boot" menu to select an OS other than W8. What happens next seems like your PC is having problems and going into some kind of boot loop. There's nothing wrong with your PC. The pretend boot has just had its bluff called. Windows 8 is paused on the threshold of resuming its hibernated state, but you've forced it to stop pretending. Now it has to un-hibernate W8, shut it down properly (like you thought it had already done), and go back into the POST/BIOS stage of a real boot process and re-present the boot menu, so that a proper chain to the alternate OS's boot loader can be executed, and you eventually end up in the desktop of your alternative choice. As long as you do everything through the W8 boot manager and you understand the above, you should get away without problems. If however you short-circuit the W8 boot manager by invoking your multi-boot choice by some other means (F8 e.g. or a third party boot manager) you have effectively "crashed" W8. Because it wasn't really shut down, what you have done is functionally equivalent to just switching your PC off at the wall and rebooting into another OS. One of the many symptoms is the fact that the "new" OS will see chaos and damage all around because W8 left the "in-use" flag (commonly called the "dirty" bit) set on all the drives it was using. Don't Panic ! The damage is illusory, but the new OS will no doubt spend the next half-hour running chkdsk confirming that fact and resetting the bits, which rather negates the 30 seconds saved by fast-boot. Next problem is when you return to W8 and it discovers that its hibernate was compromised. It might well enter its automatic repair process. Since this has been designed to give the inexperienced end-user a simple "fix me" button, it's pretty-near unstoppable, and will possibly "fix" you back to having no multi-boot options. If you've been experiencing any of the above, now you know why. The solution is to enter the Control Panel > Power Options, reveal the "currently unavailable" settings and choose "what the power button does" At the bottom of the page, scroll down to Shutdown Settings & remove the tick from "Turn on fast startup" PS All of this applies to Windows 10 too, though the solution is slightly different. You must choose "what the power button does", and then reveal the "currently unavailable" options, which will "ungrey" the things you need to change.