sudden apparition of Office Plus "activation error 0xC004F074"

After almost three years of using a laptop with windows 10 Pro and office 2010 plus, it has recently began a series of "activation error 0xC004F074" saying that ms office is not activated and a countdown of days before activation required.

What should I be looking for and where? in order to obtain that activation code that my system has forgotten about.

The system is an Acer Travelmate of my daughter, purchased thru an special high school program in 2015.