what firmware are you on? you have to re-jailbreak your device so it will boot up btw..
but if you tell me what firmware you are on then I can point you to a tutorial or just search the tutorial section on iClarified - Apple News and Tutorials
if you are on the latest iOS then all you can get is the tether jailbreak. Now if you didn't save shsh for iOS 4.3.3 or 4.2.8 and lower, then you will not be able to downgrade the iOS from the latest one.