Oh you already rooted 
Just searched for a good tutorial (http://www.android-hilfe.de/anleitungen-fuer-samsung-galaxy-s2/117451-root-anleitung-fuer-galaxy-s2.html)
Because of the market, sorry i dont know.
Have you installed CWN (Clockworkmod) too? If yes just boot into it (turn phone off and keep holding Volume up, Home and Power button pressed). Then you just factory reset your phone and delete the dalvik cache and system partitions. Just make sure you makea backup if you have anything important installed.
If it still wont work, just try to install a custom rom. You can afterwards still go back to stock rom if you want.
Enthoo Evolv ATX TG // Asus Prime x370 // Ryzen 1700 // Gainward GTX 1080 // 16GB DDR4-3200
