This issue is commonly known as a "sleeping Sola." It can happen to old and new lights alike.
Why do Solas do sleep?
The short reason is, battery preservation. Neglected batteries conserve remaining battery life to avoid deep discharge (battery damage) by hibernating. This can happen to a Sola light left in storage for an extended period of time or can it can also occur if the battery had been run all the way down after a dive and was not charged within adequate time for the battery to recover.
*Deep discharge is a term for a battery in a state of unrecoverable and complete depletion.
How to "wake" a Sola:
Plug your charger into the wall and proceed to tap the charger prongs rapidly against the light's charge contacts for 5-10 seconds, the immediately plug the charger all the way in. This surge of power can jolt the circuit, allowing the light to power back up and start taking a charge. This can take a couple tries, so don't give up the first round!
Be aware that the Sola can sometimes take up to 10 seconds to start charging even on a good day, so allow the light some time to begin charging after you've completed the tapping part of the process.
If you notice any corrosion on the prongs of the charger or in the ports of the light, this must be cleaned before the waking process can be attempted. Use this link for information on best cleaning practices. Cleaning Your Sola Charge Ports.