No electrical power at all - turn key - nothing -won't start

Solenoid. Possible ignition starter switch.

have you checked the wire that goes from alternator to the battery ,and see how many volts are going back to the battery. it maybe grounding off

If you are getting a clicking sound when you turn the key then power is getting to the starter so there is no need to worry about a relay. For some reason there just isn't enough. Check and clean your wire and cable ends free of corrosion and make sure they are all tight. It could easily be that simple. It could also be that one of the wires down at the starter is not making good contact with the terminal end,so give them all a tug to make sure.

If this is all good then I would say you are in the market for a new starter and solenoid. Hope this helps.

I think you should buy repair manual first for your vehicle after that it will be easy for you to solve the problem. Check the link may be you will find something useful here
1998 2002 Isuzu Trooper Service Repair Workshop Manual DOWNLOAD

Check the fuel pump relay and fuses it may not be getting power when you turn the key on.

Try neutral start switch. Use shop manual to determine its location on an automatic vehicle. If vehicle is a stick its attached to clutch pedal via lever. To test it remove it from its connectors and make a jumper wire and jump the circuit if car starts you found your culprit.

Yep, your fly-wheel broke. what do you need to know?

You must have #1 on TDC and the camshafts on the timing mark to fit a new belt , I rekon yer valves are fouling the piston .
Ignore the mark on the pump pulley .

have someone kick at the gas tank while you are turning key if it starts it is fuel pump

Could be one of two things.

1. Your starter motor is no good.
2. If you turn on your lights and try to start the car and they dim to almost black, then you need to check the battery connections.