I tried to JB my buddies iphone 4 on 4.1 with greenpois0n, and I got the loader app but no cydia. The loader app won't load, the screen flickers and it just won't open. After a the JB, the greenpoison logo replaced the apple logo when rebooting, but it flickered a little bit then it went back to the original apple logo.. Can anyone help get this Jailbroken?