POP or IMAP?

how do I know which it is ????

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

christ1 said

POP or IMAP?

its pop,i have the same problem again on a different install

With POP Thunderbird has only access to Inbox on the server. Any folders you created on the server remain invisible. This isn't a Thunderbird problem, it's just how POP works.

You'll need to set up your account(s) as IMAP in order to get access to any other folders than Inbox on the server.

Note, you cannot change an existing account. See http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account