Sunpak 383 just died?

My sunpak 383 which I've had for 4 years but have used lightly seems to have died.

With freshly charged rechargeable AA batteries, when I turn it on, it makes that high-pitched charging sound for a few seconds and then goes silent. Ready light never comes on, and can't test fire by pressing the button.

Any ideas what it could be or if it's an easy fix?

Funny how I just ordered a Metz 50 af-1 as this happened, but I was hoping to have both flash units available.