Flooding can occur after using cleaner on the intake or if you left something disconnected. You can pull a plug and check if the plug is wet with gas too. Common things left off would be the vacuum to the FPR, the MAF connector, the ECT connector, the TPS connector...
If it fires up and then dies from flooding again after unplugging the fuel pump relay to clear the cylinders, then something is causing still causing it. If you don't see anything amiss, try checking the fuel pressure.
If it just won't fire up, static timing or fireing order are still suspect.