I have repeatedly had to reinstall Thunderbird to my computer to get my e-mails.

Why?

It seems to happen each time I shut the computer down.

What exactly happens when you shut down the computer?

It seems that when I close the Thunderbird program or shut down, I must go to the start program to open it again and then I can only see my folders but nothing will open when I click on it. The only way to fix it is to reinstall Thunderbird again and then I can get to the individual messages and folders, etc. It doesn't lose anything, I just can't get to them unless i do a complete reinstall?????????

I must go to the start program to open it

Please explain that in more detail. How exactly do you start Thunderbird?

Are there multiple Windows user accounts?

When installing Thunderbird, are you using a different Windows user account than when you normally run Thunderbird?