Toyota Repair: 1990 Toyota Pick up truck v6, amp fuse, alternater

Question
My truck has been having electrical problem a lot lately and I got a new alternater and had it tested to make sure it was good and it was and I got a new battery and when I brought it to the mechanic he said the alternater and battery are both good. I put the battery back into my truck and it started right up but when I got back to my house I went inside to eat and when I came back my truck wouldn't start up again. It sounds like it wants to turn over and start but just won't. So I've boughten a new battery, alternater, and put in a new 80 amp fuse back into my truck for the alternater and can not figure out what keeps going wrong. I've unhooked all my stereo equipment including my amp. My battery light used to stay on in my truck also but by putting in my new alternater it got rid of that problem and now turns off. I was hoping u could help me and my dad figure out why thus keeps happening. I think maybe everyone is wrong and my battery is just a.p.o.S. lol but I also wonder if its a fuel injecter, distributor, spark plug, fuel pump, or starter. PLEASE HELP!!!!

Answer
If the starter only makes a clicking noise when turning the key to start and the headlights stay bright at this time then most likely it's a bad starter, this is common on these older  4runners.
If the battery is completely dead and the lights don't even come on then it's a power supply problem, dead battery or bad connection at battery. So it's very important to let me know exactly what happens when it doesn't start, does it not turn over, are the headlights bright, does it turn over but not fire up?