Some people have had problems with their iPod Touch after it was jailbroken, such as errors, the Apple Logo Loop screen, and blank screen or restore errors. These errors can usually all be solved by placing your it into DFU Mode and restoring it through iTunes.
DFU (Device Firmware Update) Mode puts your iPod Touch into a mode that allows you to solve many problems. When it is in DFU Mode, it bypasses a built in program called iBoot. iBoot is a tiny piece of software that makes sure you are restoring a firmware version greater or equal to the firmware currently running on the iPod.
While in DFU Mode, the iPod Touch will not load the iBoot Software or the operating system (OS). Even though iBoot or the OS are not being loaded, your iPod Touch can still work with iTunes. This will enable you to downgrade the current firmware on the device, or to restore it.
So, if you have a jailbroken iPod Touch that will not boot, is getting errors, and so forth, then you should try to put it in DFU Mode and then restore it.
Connect your iPod Touch to your computer via the USB cable, and then open iTunes if it doesn’t open automatically. Stop any syncing with your iPod Touch. Press the Home button on your iPod Touch and then slide the slider to Off to turn the iPod Touch off.
With your iPod Touch turned off, hold the Power and Home button simultaneously for exactly 10 seconds.
After 10 seconds, release the Power button, but continue holding the Home button for approximately 30 seconds, or until iTunes displays a message that iTunes has detected your iPod Touch in Recovery Mode (which is DFU Mode).
Follow the same restore steps above to restore the iPod Touch.
If you are having problems, make sure you are holding down both buttons and then release the Home button right before you think the Apple logo will appear. If you see the Apple logo appear and are still holding down both buttons, you have held them down for too long and it will not work correctly. You will have to try again until you get it right.