HOW TO REBOOT IPHONE & IPOD TOUCH AFTER JAILBREAK: Tethered Jailbreak – this means that if you EVER reboot, restart or lose power to your device post jailbreak, then you will need to boot your device up connected to a computer to enable the Jailbreak functions to work.
The device itself will boot up normally without this ‘tethered’ connection, however, all Jailbreak features will be disabled, and also due to the aforementioned changes in architecture, some native iOS services will also cease to function, with the most prominent being mobile Safari browser. This is not as daunting as it seems, as the Jailbreak tool will generally have ‘boot as tethered’ option which simply patches the kernel again (temporarily until next reboot) and boots the device up.
Step 1: From the main RedSn0w menu click the Extras button.
Step 2: Select Just boot from the Extras menu to boot tethered and follow the instructions to put your device into DFU mode again for boot.