Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
To start with, I need to know what type of computer you have, a Windows XP, Vista, Windows 7, or Windows 8 or 10?
Or do you have a mac?
Also, is it only your gmail messages that are missing, or are you experiencing other issues?
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.