I am sort of OK with computers and can follow instructions, but I so not clever that I understand the techie details and whys and wherefors of connecting to and using servers. So I am asking for help with this problem.

OS Version: Microsoft Windows 7 Home Premium, Service Pack 1, 64 bit
Processor: AMD Athlon(tm) II X2 245 Processor, AMD64 Family 16 Model 6 Stepping 3
Processor Count: 2
RAM: 3839 Mb
Graphics Card: ATI Radeon 3000 Graphics, 256 Mb
Hard Drives: C: Total - 400001 MB, Free - 223921 MB; D: Total - 11313 MB, Free - 1153 MB; G: Total - 199996 MB, Free - 159964 MB; H: Total - 399993 MB, Free - 399889 MB;
Motherboard: FOXCONN, 2AAF
Antivirus: avast! Antivirus, Not Updated

I live in France, using orange.fr as my ISP. At the beginning of September, Orange locally had a major service outage, which took an hour or two to restore internet connection. My email client, Thunderbird Portable was open at the time. Since our broadband has been reconnected, I can no longer send emails with smtp.orange.fr, or receive emails with either pop.orange.fr (what I usually use) or imap.orange.fr.

Originally, I'd thought that it was my copy of TB was the problem, but when installed on other computers, I can call down and send email with orange.fr.

However, I also use another server on my TB Portable - gmx.fr - and imap.gmx.fr calls down emails with TB without problem.

When trying to receive emails, I have no messages for x@yz email address
and when trying to send emails, I get a small window with "Sending of message failed.
The message could not be sent because the connection to SMTP server smtp.orange.fr timed out. Try again or contact your network administrator."

I have managed to do a telnet test: telnet pop.orange.fr 25. The response was "421 cannot connect to smtp server 80.12.242.14 (80.12.242.14:25) NB connect error 1460 connection to host lost."
This apparently means that my ISP is blocking me, but that is rubbish as I can send and receive emails using Thunderbird Portable on another computer in the same room using the same connection settings, so the problem is definitely concerns this computer and not the connections to and from the ISP.

Thus it would appear that there is now some corruption in the interstices between the signals entering my computer and being available in TB.

I would be very grateful if some clever person would guide me through solving this problem. Having no email other than on a manky phone is not much fun.

Check the server IP address as nothing exists at that address.
Also ensure it's not "hard coded" into your Hosts file.