Here is a rudimentary check list to work through

  1. Did you use the original loom and if so did you disable any built in burglar alarm/door switches etc., thus enabling the ECU on an injected system or spark ECU system - needs a yes or actively OK
  2. If a 3rd party loom, are all of the essential features connected - needs a yes
  3. If the donor was injected with a catalyst, have you included the Lambda sensor in the exhaust - needs a yes if running with the ECU to get power but will not stop you starting the engine
  4. Is the pump working - needs a yes - it should operate for up to 30 s on switch-on with an ECU but cuts off if the engine is not running in case there is a leak to avoid fires
  5. If injected, have you connected the supply from the pump to the correct end of the fuel rail - i.e the one without a non-return valve on it - need a yes
  6. Is the engine getting fuel - needs a yes
  7. If injected are the injectors connected correctly - needs a yes
  8. Are there any sparks available - needs a yes
  9. Are the spark leads connected to the appropriate cylinders - needs a yes
  10. Is the engine timed on the correct stroke if on a distributor with points - needs a yes

If you have achieved all of the yes requirements above, then there is little reason why the engine will not run, so hopefully this gives you something to go for in the immediate future.