Windows live mail will not pick up messages from the server

I downloaded a version of Live Mail from Windows Live Essentials, as the mail programme shipped with Win 8 is rubbish and I need POP to manage my life. I set it up to communicate with my gmail server and initially it worked OK. But every time the PC is shut down,e.g. overnight, and every time we change user accounts, Live Mail will  not pick up any of the messages that have arrived at the server in the interim, and I have to log-in to my Gmail interface, re-send the new messages to myself, and then and only then will Live Mail pick them up. If the PC is on and remains at the same user account, the pick-up works fine. I have checked the settings in the account set-up, and everything is correct, but this unreliability is driving me mad, I don't trust the program, I have to check the Gmail at the server constantly to ensure I don't miss stuff. Can anyone help?