my lipo dischared ones .. then i charged on nimh mode ... only one cell charged properly... is there any way to charge both of them??? as i feel other cell is not damaged.. 
when i connect in balance mode... charger shows over voltage for 2nd cell
battery is 2s lipo

Are you unable to charge the other cell?
It sounds like the pins on the battery's balance connector aren't making good contact. Suggest you pull each pin from the plastic housing, clean off the contacts and bend the contacts in so they get a better scrub/connection when plugged into the charger.
Only do one pin at a time! Once, I had all four pins out of the housing and shorted two while working on another. Yes, the battery caught fire. I put it out before any explosion. (Did I mention I lack common sense? I won't comment on what kind of degree I might or might not have.) That pack was a total loss.