@enes, Windows 8/8.1 does not require a machine to support, or have enabled, secure boot. I have a Mac which does not even support it and it boots just fine. Here's some good suggestions:
1. Press f2 or f12 (I think); f2 should open the BIOS itself, and f12 should open the boot manager. However, I'm not exactly sure about that. Note: Do this as soon as you press the power button! Hold it down until you see complete white cover your screen. Go into the boot category, and turn on EFI boot. If its not in that category, move around the bios with the left and right arrow keys until you find it. Left and right
arrow keys move through categories, up and down arrow keys navigate options. Enter edits an on/off value, and f5/f6, or in one of my other computers case, f7/f8 changes values which have multiple values. Set EFI Boot to on. Press f10 and then select yes to save your settings, or go to the 'save and exit' category and select 'save and exit'. Press the up and down arrow keys to find "yes", and press enter. Your computer should reboot automatically. You should be good to go then.
2. Reinstall windows. It may be that your computer has "forgotten" windows, or "crashed" as some people call it. Note: Reinstalling windows is a very difficult process!
3. Send it into the store for reparation.
Note: Do not, under any circumstance, go into the BIOS unless you know absolutely what you are doing. Sited assistance is required. If you go into the BIOS, and do not understand what any of the options do, press control alt delete immediately to exit the BIOS and continue the boot process normally. Editing the BIOS settings without knowledge of what you are doing could have disastrous results, which includes failure to boot properly, your computer beeping at you, indicating in invalid option, blue screens randomly when your not expecting them or at a particular boot stage, failure to recognize a required or necessary device, failure to recognize the RAM/hard drive, etc.
If you do suggestion number one, make sure you have someone close by who actually knows what some of the options do.
A good suggestion when in the bios is: When you don't know what an option does, don't mess with it.
"On two occasions I have been asked [by members of Parliament!]: 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out ?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question." — Charles Babbage.
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