Car Electronics And Audio

I've checked all the connections and everything is wired right and tight. I'm on a bit of a budget so my entire system is Boss Audio. I have a head unit and a 5 channel amp running 2x 6.5" speakers, 2x 6x9" speakers and a 12" sub. The amp is 2900 watts (1400 RMS) and even though i don't know a lot about electrics, I've been told it's plenty big enough and each channel should have plenty of power for each speaker. I used a 4 gauge wiring kit to rig it all up too. I can't work out why it turns off. Should i take them all off and put them back on one by one until the problem occurs or should I use a voltmeter? If so, where do i get one and how do i use it? I would really appreciate any help. I've tried all I can do and it's starting to do my head in. I just wanna use my stereo.