Me and a mate recently hooked up a Amp and Dual Subs and everything was working fine.
Next day I go turn it on and realize there is no bass so I go to the trunk and notice my amp has no power on it.
I then proceed to check everything. Making sure everything is wired properly and tightly, still to no avail so I disconnect my head unit and notice that the amp turns on however when I reconnect my head unit the amp turns off.
I don't have another head unit too test on but I don't want to fork out for another unless I have no other choice.
Disconnect the head unit, then touch the REM wire on the amp to the +12VDC line, and see if it comes on. Make sure the gains aren't turned all the way up, causing the amp to enter thermal protection mode. If you have a DMM, check the head unit to make sure you're getting +12VDC from the REM trigger wire when it's turned on. Make sure your subs aren't presenting a load too low for the amp's minimum impedance rating.