I recently upgraded my psp 2000 ver 3.71 to ver 6.20, but now its not able to play the copied games. What should i do now??

Ofcourse its not, and that always a factor you should think about before you upgrade, playing backups is not something Sony will endorse and well now i guess you will have to wait for another custom firmware, or just use a Pandora battery if your PSP 2000 supports that, because not all psp 2000 does that... well i guess you could just Google that.. and remember to read thing thoroughly before ever upgrading again!