In GEO3NEX open Help → License. If a computer cannot reach the licensing service, use Advanced / Offline activation and contact O3NEX with the machine id shown there.
"This license is already activated on another computer" means it is in use elsewhere. Contact O3NEX to release the previous computer.
GEO3NEX keeps a recovery copy of unsaved work. After an unexpected shutdown it offers the recovered copy at the next start; your original file is never overwritten.
Support contact details are available from O3NEX.
O3NEX