When trying to activate Windows 10 if you get an error code 0x80070005, then its an issue with UAC or User Account Control. The error message would say:

Access denied. The requested action requires elevated privileges. 0x80070005

Applied or both KMS client/ MAK and KMS host, You need to make sure that SLMGR, command line tool used to manage Windows activation, from an elevated command prompt.

Open Command Prompt with admin permission, and then run slmgr.vbs. This will make sure that activation goes through smoothly.