Sorry to hear that! What's the battery voltage reading on the ToneWoodAmp when you do get it to power up? It should display at power up.
Make sure you're changing all three batteries. If one is stuck and only two are being changed, you'll experience intermittent power issues. If the third does happen to be stuck, loosen the screws on the bottom of the TWA near the battery cover about a quarter turn. Let me know if this helps!