Have 'lost' inbox

Good day Thunderbirds I seem to have done something rather disastrous. This morning when starting up my inbox is empty and though i have sent test messages from other mail platforms and they arrive in my Gmail account they are not downloaded to my Thunderbird. I did change the Gmail conversation option, because i want each mail to be separated. The combining of all related mail confuses me. I have reset the option but nothing has changed. All the other folders are intact and if i open "All Mail" every message is still there including the added test messages. Can anybody figure out what i have done and help me restore my Inbox? What if i re-install Thunderbird or something like that? Here's hoping. I really do not want to access my mail online via Firefox. Thunderbird is my only way of managing 158.0mail.