I just bought my Raspberry Pi 3 today and it was working fine while I was trying to install the micro-SD card. After turning it off about an hour for some odd reason, it did not respond! It showed the red light, was getting enough power and everything, but all I got was a blank "no signal" screen on my monitor.
It was a Raspberry Pi 3 model B with a Canakit case. I may think it has something to do with the fact that I had just installed heat sinks. It worked fine before I installed them, but I'm pretty afraid that if I try to take them off it'll rip everything else off too.