If you are using Etcher it will take either type of file (.img and .zip).
It will convert the zip to .img automatically and then flash the .img to the SD card.
You can tell if the SD card is loading on boot by looking the the ACT GREEN LED on the raspberry pi. It will flash on and off during boot. If the ACT LED is not flashing then you might have burned a corrupted .img or .zip file. I would download the image again.
The other way to check is to connect a HDMI monitor to the raspberry pi. It will show a boot screen with status information. If nothing shows up on the HDMI monitor then the image on the SD card is bad.
The Raspberry PI has a LED called PWR that is RED (Power indicator LED). When it is ON and solid RED it means that the power supply is running at 4.8V-5.2V to the Raspberry pi. When it is blinking RED that means the power supply is having trouble supplying 4.8V to the Raspberry Pi.
The other problem we have found is that some power supplies have bad microUSB connectors that are loose when plugged into the Raspberry Pi. If you wiggle the microUSB connector slightly and you see the PWR LED start to blink or turn OFF. This is an indicator that your connector is bad and needs to be replaced.