Question about jailbreaking my ipod touch?

so i jailbroke my ipod touch 4g a few hours ago and i used the green poisin to do it and it worked and then i clicked on cydia from the loader, but the problem is cydia isnt downloading? it just keeps saying "initializing filesystem (will exit when complete)" on a black screen and it exits (and restarts my ipod) after that but every time i click on it it says/does the same thing? it wont download all the way for some reason? do you know how to fix it or do you know how to delete cydia? also do you know how to unjailbreak my ipod without losing any of my previous data (pictures,music, etc)? thanksomuch!