Personal folders constantly disappearing in Windows Live Mail

I have been using Windows Live Mail for many years and have never had any problems. However in the last 6 months I have lost all of my personal folders several times. All my e-mails from these folders are then downloaded from the server again next time I open Mail so I end up with 900 items in my inbox. It only downloads messages for the last 6 months however, so anything that was in my personal folders prior to that time is lost. Does anyone know why this happening and how to stop it? I am losing important e-mails and it is driving me insane! I am running Windows 8 and have McAfee virus protection running.