after closing laptop, t-bird no longer shows text when I open an email. CAUSE: unknown - problem solved itself

T-bird opens mail and goes to inbox. But when I click on an email, the screen is blank, no text anywhere. My laptop was closed for several days and restart did not fix it. Can I update t-bird without losing my inbox, saved messages, etc? more info... 1. just did a PC system restore to 3 days earlier. Opened my mail, same problem. 2. located the T-bird installation file and "re-installed" it. Opened mail, same problem latest info... Probable cause: when I closed my laptop, T-bird was open. The 4 messages that I received earlier must have been corrupted somehow. I can now send/receive new messages OK, and now those 4 (corrupted?) messages have disappeared from my inbox.