Can't access imported mailboxes in Apple Mail

[bizzo]

Alright so I recently upgraded the hard drive in my macbook and reinstalled OS X. I imported my mailboxes that I had setup on my old mac hard drive. The folders show up in mail but the program wont let me click the drill down to access them but for some reason if I drag a mail item from my inbox and hover it over the drill down for the imported mailboxes it expands them and allows me to put the mail in one of the imported mailboxes. No matter what I do though it won't let me access the folders or the mail that's in them. I hope what I've said makes sense and if not let me know and I'll explain further. I'm pretty good with computers but this is my first mac in over ten years so I really don't know the in's and out's and I can't find anything in the settings that will allow me to actually access these imported mailboxes. Any help would be greatly appreciated.