Windows 8 and 8.1 tend to load so quickly that it is most difficult (quite often not possible) to boot into Safe Mode, one thing that does sometimes help is pressing Shift + F8, if you have a Windows 8/8.1 disk and the computer concerned has an optical drive (DVD) you should change the boot sequence so that it boots from that first and the HDD second, place the installation disk into the drive then restart the computer, this should get you into the system repair etc options.
What happens if you try and boot the computer as you normally would and why are you running chkdsk in the first place, it is not a tool that needs or should be overly used as it is intended for diagnostic use when things have gone wrong.
Please provide information about your computer, this includes is it a notebook or desktop, is it a custom build or brand name such as Dell or HP, if it is a brand name provide the model name or series number (not serial) if a custom build post as many hardware details as you can, providing these details will enable us to better assist you.
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