Get the cells apart individually and test their voltage. A fully charged cell should be 4.2v, and settle down to 3.7v after some use.
If you have any cells that measure a reverse charge, they're damaged and should be tossed. If any of the cells have a very low charge, you can try and recover them, but you'll need a current or voltage limiting supply.
For a current limited supply, set the voltage to 3.7v and a current limit of 50-100mA and try charging the battery. If the voltage does not steadily rise, or if the voltage on the battery quickly falls off when the supply is removed, the battery is bad. If the battery manages to get to 3v, you can kick the charge current up to 500mA.
For a variable voltage supply, measure the voltage of the battery and set the supply voltage 0.5-1v above the battery and monitor the current going to the battery with a multimeter, you'll want to keep it in the 50-100mA range until you get to around 3v and then you should be able to kick it up to 500mA by increasing the voltage output.