Car Audio Help

[gettysburgfreak]

I am hoping there are some guys here with knowledge of car subs/amps. Here is my current set up:

2 12" Kenwood 4-Ohm Single-Voice-Coil Subwoofers in a ported box.

My amp is an American Legend 600 watt that my friend gave me for free and I think this is the root of my issue.

About two and half weeks ago I went to Best Buy bought the subs, box, and wiring and had them install everything. System worked great for a week or so then one day I go to get into my car and the subs didn't work, the amp was not getting any power. I took it back to Best Buy the guy looked at it said the amp was dead, fiddled with it and somehow got the amp to work again. System worked great for another week or so until today. Worked fine this morning, went to leave later in the day, no power to the amp again. Does anyone have any ideas what could be the issue? I checked the fuse on the amp and its not blown.