I have a 1990 Ford F150 8cyl 5.0 that I can't seem start ?

[Shannon]

What was happening to begin with was: I tried to start it and there was a buzzing sound. I thought maybe the battery was too low so I got a new one. I tried to start it and it was still buzzing. Then It sounded like it was coming from the starter solenoid so I replaced that. No such luck it still won't start. Then I thought maybe its the starter so I took it off and had it tested. The auto store said it worked fine. So I put the starter back on and tried to start it again but it still won't start. I had a friend get under the truck to see if any power was even getting to the starter and apparently its not. So since then I have checked the ground wire to the starter solenoid and that was fine. I've tried the screw driver trick while banging on the starter solenoid and trying to start it and it still won't start. Now I'm pretty frustrated and can't seem to figure out why no power is getting to the starter. If anyone has any ideas please let know.