Issue with double din head unit

I've had my Jetta for about 4 years now and had a double din pioneer unit installed at Best Buy with an amp and subs. Everything worked since i had it installed, Now my pioneer takes like 20 mins to cut on after i have been driving, and then it cuts off, and powers on and cuts off like its trying to get power. It will eventually cut on and stay on but if i down shift sometimes or even cut my Air conditioning on it cuts off, pretty crazy. It seems like maybe the wiring or possibly a fuse? I'm not too sure. Does anyone know where i can possibly start to fix this? Any advice would help. thanks