Is it asking for a Thunderbird password? That would be most unusual. Pr is it asking you for the password for the mail account you are using to send mail. Much more common, especially if you have an antivirus program that scans email as when they drop the ball your connection times out and you are asked for a password to reconnect

Here's the message I get when I try to send an email:

Unable to authenticate Outgoing server (SMTP). Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'.

When I look in Account Settings in Thunderbird, I see:

When managing your identities you can use a server from this list by selecting it as the Outgoing Server (SMTP), or you can use the default server from this list by selecting "Use Default Server".

Below, in a text box, I see: Comcast - smtp.comcast.net (Default)

There are active buttons next to that. One says ADD... The other says Edit...

Further down is additional text including my User Name (aka my email address) and Authentication method: Normal password

Someone please help. Micro Center in St. Louis Park, MN did the diagnostic regarding the PC's going offline every few minutes. The Repair Summary says "passed hardware testing" and "pc should be in working order." One person suggested that based on the Internet problem complaint the service person probably wiped all passwords. I can't find any written record of my Thunderbird password, so I now can receive email, but I cannot send email.

How do I reset my password?

I have now found my original password in my book of passwords (under Mozilla, not Thunderbird.) But, I still cannot send an email.

I get the same message as before: Login to account "Comcast" failed. And this message: Login to server smtp.comcast.net with username bobking10@comcast.net failed.

Solved.

Above, Matt said "Pr is it asking you for the password for the mail account you are using to send mail."

I thought I was using Thunderbird to send mail!!! Further info from a Google search revealed I'm "using" whatever follows the @ sign on my email address to send mail.

Very confusing for someone who's not computer savvy.