In your Speedlight you can use 4 AA sized batteries.
Alkaline, Lithium and rechargeable NiMH batteries.
Be sure your batteries are charged, or new. Never use different type together. So all 4 should be same brand, same capacity and same date.
When you did not use the speed light for a long time, two things could have happened. The contacts in the battery holder are dirty, or oxidised or the capacitor for the high voltage has leaked or dried out.
The contacts you can clean if they are not oxidised to strong. Never use sharp tools to sanding paper to clean contacts. Just use a dry cloth. It the contacts are really dirty, put some contact oil on a cotton swap and rub the contacts for a while. Make sure you rub all the oil away, using the dry cloth.
If old batteries, can't make the Speedlight sing, yes you should hear an oscillator, the on / off switch can be dirty or oxidised. If the oscillator runs, but the ready light does not go on, the capacitor is gone. Needs a technician to replace the cap.