That blink is usually the charger saying the pack is too low or out of temp range after sitting. Start simple. Bring the battery to room temp, wipe the contacts on both the pack and charger with a clean cloth or a little alcohol, then make sure it is fully seated. Unplug the charger for a minute and try again.
If you have a meter, check pack voltage. If it reads near zero the internal protection may have opened. If it reads well below what the charger expects, sometimes a few insert remove cycles will coax it to start. Try a different outlet too.
If none of that wakes it, the cells may be too deeply discharged to recover safely. At that point do not force it. Recycle the pack or see if the maker will warranty it if it is still within coverage.
