Shoutbox

As far as I know, that screen means "Your iPhone/iPod touch needs to be activated within the iTunes program", I guess you have updated it from iTunes even it being jailbroken, or the data inside it went corrupt (happened once in my nano)

I'd try what andrey's result says; put it in recovery mode (turn it off, connect the usb cable again while pressing the home button) so that you can restore it.

Note that restoring it will erase all data, not a problem if you have a backup within iTunes. Also, you'll be able to jailbrake it normally.