Support (and updates) for Windows 8 ended on Tuesday, 12 January 2016.
If you cannot access the Windows Store, you cannot upgrade to Windows 8.1. Since Windows 8 is no longer supported, you have two (2) options:
OPTION A: Attempt to upgrade the Win8 computer directly to Win10 using the Media Creation Tool and (Win10) ISO. Start here: http://windows.microsoft.com/en-us/windows-10/media-creation-tool-install
- Valid, legit Windows product key is required!
OPTION B: Purchase a full retail version of Windows 10 (US$119.99 & higher) then format the hard-drive & do a clean install of Win10.
Once more...
Your Win8 computer should NOT be connected to the internet or any local networks (i.e., other computers) in its current state. All business & personal data (including online banking & credit-card passwords) should be considered at-risk, if not already compromised.
Good luck!