im confuzzled, Amp gets power, but when grounded it doesnt? Options

[LimitedST]

Alright. im waaay confused.

Heres my situation
i got my amp in the trunk.
The power from the battery in the engine bay travels from their to the trunk. the coords from the head unit also do the same. Now the grounding wire that came in the rockford fosgate amp kit, is only like.... 8" long, its not going anywhere but in the trunk.
So, i found a screw already grounded, inside the place where the jack goes, put the ground wire there, gscrewed back in... no power? decided it was a bad ground.
moved it. drilled a tiny little hole under the carpet, next to the place where the jack goes. screwed it in. no power?

unscrewed it. turned car on. it has power....

The amp will turn on when not grounded, but when it is grounded it wont turn on.
The amp will turn on, but wont send signals to my speakers or amps. so i dont know what its doing.
im really confused. and any information would be helpful! thank you.
limited.

fye amp = p3002 subs = 8" phase 1
speakers = 6 x9 40ways

rockford fosgate of course

[Jap6g]

with my sub i attached the earth wire to my rear strut, did you earth you amp first? my mate did battery first an it didnt work so he earthed it without connectin anythin for a day an it worked wen he hooked everythin else up. jus try earthin it an nothin else