Hmmmm... I know on the Mac you get that message if you hold down the option key (alt key) when you launch iTunes. This is useful if you have multiple iTunes libraries.
I'm not sure why you're getting that message if you're not pressing down on a key. Just select your iTunes library, make sure it loads, then restart the software and hopefully it should be fine. You didn't delete your library or move it accidentally, did you?
No, nothing like that... but it seems to have resolved its self - i clicked quit and opened it up again - no problems at all now.
thanks for your help tho!