I just reinstalled Windows XP on my C drive. Before reinstall I moved everything in needed to keep to my S drive(my second hard drive). One of these programs was Firefox, and it had many messages in the inbox which I needed to keep. After moving the entire program to the S drive, I double checked that it worked before reinstalling. Now when I run Firefox it just prompts me to set up a new account, and all the old info is gone, including all the old emails. Where did they all go and can I get them back?
Firefox is a web browser, not an email client. This may be a factor in your problem.
Assuming you actually mean Thunderbird, this link describes how to back up and restore a profile (though it may be a bit late in this case).
These appears to be some useful general case email restoration info.
Assuming TB and 2k/XP, your info should be in C:\Documents and Settings\YourName\Application Data\Thunderbird\Profiles. If you backed that up, then you need to tell TB where it is somehow. If you didn’t… that would be bad.
Oops, sorry. I do that all the time. I was referring to Thunderbird.