I have a lipo turnigy 3s 1500Mah . The charger refused to charge it. When saw the voltage readings it showed me two cell below 3v and one at 4 v.!
How to get back this lipo working.?

carefully,

If you discharge cell below 3v , it cannot be recovered.

But if it self discharged then you can carefully give it a try to give a small charge and see if the cell recovers to above 3v

Else this lipo is waste, remove one cell which is more than 4v

I have IMAX charger.! In which mode should I charge it .?

the most possible way to recover is ; charge the lipo on nimh mode and inject some amperes in it like 400-500 with out attching balancer leads.
then give a try again on lipo mode.
if still dont work, do whatever u want to do(throw it or keep it)

I guess I will have to throw it

Open up the lipo if individual cells are gone you might be able you use if any cell is still holdig charge. You will need to take the good ones out and solder them in series to get a 2s battery or just keep them for future if any other battery dies down. I have posted whats inside a lipo in some other post on rc india..you might have to search for that post. but in all probability you might be able to salvage atleast a singlr cell out of the pack

dont throw it! jiust connect a 9V batry to it fr a min or so...and then connect to d charger if it isnt detected just connect d batry to it again...
I did the same to mine and its still working !

Which 9V battery.

I'm thinking of a method wherein I will individual force the cells to get charge above the require voltage by nimh mode. As my cell 1 and 2 are below limit then I will force charge them to 3 v.
But how to charge this cells individually .?? Any idea.?

Charge usin the jst balance connetor. The black lead is the negative...there fortg each lead is connected to the positive of the next cell. Hope that helps

9v batry used for transistor radios... which has +ve and -ve on same sides..

Ok now I tried forcing the battery to get above voltage using nimh mode.! I got battery voltage of 2 1.9 and 4.5 volt. The charge detected correct number of cells but due to high voltage in 3 cell it says batter voltage error high voltage error