amp problems

O.k listen to this. two days ago I started having problems with a four channel amp(American Pro) it would power up for about 1sec and then power down. If I turn off the power then turn it back on, it would repeat. I removed the amp and replaced it with another and it works fine but the american pro still is bad. Later on that night I looked over my wireing to see if there were any frayed wires or lose connections. I checked the fuse next to the battery, and  in the inline fuse just before the amp, all were good. I checked all the speaker connections and the rca jacks all of those were good. When I tried to disconnect the 2channel(Visonik) amp I used for subs, it started turning on and off rpeatedly for as long as it had power. I turned it off removed the screws that held it in place checked the connections on the amp and the subs, all were good and tight no frays and no loose connections. When I turned on the head-unit, the amp started smoking, within seconds flames started coming from the amp. Now what I need to know is what causes this so I can solve the problem. I just brought a $300 digital audio 1 ohm stable amp. I don't want the same thing to happen to this one. Has any one experience this and if so what was the cause and how did you solve it. My amps were screwed directly into the floor board of my explorer. When ever the amp was switching on and off my interior lights would dim, the amp and the interior lights would flash together. The amp would switch on and off and the lights would dim insync with the amp. Could some one please point me in the right direction.