I recently jailbroke my ipod
touch 2g running on 4.2.1 firmware using greenpois0n and i purchase the cydia app using loader and i restarted my ipod
then saw the cydia app and i tried openning it but it doesnt open any solutions please help!!!
reboot it again.
if that doesn't work, rejailbreak it with redsn0w0.9.6rc8 right on top of your greenpois0n and just pick to install cydia. it's a pain but it works to install cydia.