Media library not detectiong uploaded images

Hi everyone

About six months ago i changed hosts and i exported my wordpress blog using the export/import function, all went well but im facing some problems.

im want to change my blog layout to something near a magazine layout and i want to use the post thumbail function. ive read the wordpress codex and found how to do it and it works, post thumbanil + post excerpt…but when assigning thumbs to posts wordpress cant locate all the images i uploaded before i exported and imported the blog, i found out that i had to backup my database and import it instead og using the wordpress export format, is there a way that i can make wordpress aware of all the previosly uploaded images?

Thanks a lot