As RolandJS posted if the factory recovery partition is intact and the computer was pre-installed with 8 you can do a factory reset by tapping a key at boot. What is the make and model of the computer?
OEM computers with Windows 8 or 8.1 pre-installed has the key embedded in firmware. After a clean install the computer will self activate once online. You can create a DVD or USB flash drive installer user the Media Creation Tool. There is a version of Windows 8 called Windows 8 with Bing. If you have this version the Media Creation Tool will not work.
If you can boot to Windows then use the FirmwareTablesView Utility to find your key. Look under the MSDM table. You can verify that it is the same using Produkey
Write the key down just in case the install asks for it.
Edit: Once you boot the install media do a clean install per this guide.
Edited by JohnC_21, 11 October 2016 - 02:38 PM.