Using the Greenpois0n RC5 untethered JailBreak tool on Windows allow you to jailbreak the Apple iPad at the iOS 4.2.1 firmware. The guide below will provide a "step by step" or a "how to" for JailBreaking your iPad on iOS 4.2.1 using Greenpois0n RC5 tool.
How to Jailbreak iPad 4.2.1 using Greenpois0n RC5
Step 1: Download Greenpois0n RC5 Jailbreak for Windows.
Step 2: Once the download is complete, open the zip file to unzip it to the Desktop.
Step 3: Open folder and double click Greenpois0n.exe to launch it.
Step 4: Click on the button ‘Prepare to Jailbreak (DFU)’.
Step 5: Greenpois0n will display the instructions to put the device in DFU Mode
You will be asked to press and hold the sleep button for 2 seconds.
Continue holding sleep; press and hold home for 10 seconds.
Release sleep button; continue holding home for 15 seconds.
Step 6: Once your iPad is in DFU mode, click the Jailbreak button.
Step 7: Greenpois0n will now jailbreak your iPad 4.2.1.
Step 8: Click the Quit button once the software application has completed.
Step 9: After the iPad restarts you’ll notice a new Loader app on your Springboard, entitled “Greenpois0n”. Press to launch it.
Step 10: Press to select Cydia then press the large Install Cydia button that appears.
Step 11: Once Cydia has installed successfully on your iPad, you will be prompted if you want to remove Loader from your device. Press the Remove button then press the Home button. Your iPad will now reboot.
Your iPad is now JailBroken. Those who are facing any issue while jailbreaking iPad on iOS 4.2.1, please feel free to comment below!
Related: After you JailBreak your iPad. be sure to check out my best Cydia apps for the iPad.