Isuzu Pick Up Mod 95.

Hello, is there anyone who can help me diagnose why my truck won't start? It's a 1995 Isuzu 4x4 pickup. Initially, the timing belt broke, and it's now been replaced, but it starts and almost immediately shuts off. The mechanic says there's power, but not enough, and the scanner didn't show any codes.
If anyone could give me their opinion or guide me toward the likely problem, thank you.