Answer

OEM Windows 8/8.1 comes preinstalled on notebooks and Windows will complete the activation process on-line once the notebook connect to the internet for a minutes.
However, there are many reasons which would affect the Windows activation.
If you've got the Windows activation error code, find the error code in the FAQ table and follow the instruction to solve the problem. (http://www.msi.com/faq/nb-1624.html)
If you’ve made a hardware change (upgrade/repairment), please contact with MSI local service center.
If you’ve installed a different version of Windows (e.g. retail version) yourself, please contact with Microsoft Services.

Otherwise, please try the Windows phone activation service to re-activate your Windows. (Find the phone activation instructions in the attachment file)