ok
the story like this

i bought a OEM 8.1 single language from C-zone
install on to my illegear(in case you guys ask on what comp)
activated  on 8.1windows

then last week prompted a msg from windows saying that got free Window10 upgrade.. so i upgraded
to windows10 , then when i check the activation there saying that my CD KEY is invalid, i tried to put it again and the system said that my key is not usable asked me to get another new