2 things.
1, The past tense of Jailbreak, is Jailbroken.
2, connect your device to your PC or Mac, hold the home button and top button for 15 seconds untill your device disconnects,
leave for a few minutes before pressing the top button to start the device normally, iTunes should recognise it as normal, in which case its working
or in recovery mode, if it is in recovery mode then you can resore to your origonal firmware.
If niether of these work, then leave your ipod for 24 hours, allow the battery to completely drain, so you can find out what mode it is in
then connect to your Mac/PC and see how iTunes reacts
you should find your ipod in recovery mode, or more likely with damaged or incomplete firmware,
to fix this press shift+restore (on PC) optn+resore (Mac) in itunes and restore to your previous firmware,
Hope i was of some help

Mike