how old is your battery?
is a original or aftermarket radio?
well if you battery is older like 5 years may be is time to replace that.
if you radio is a aftermarket make sure was installed correctly
try checking the alternator try charging the battery with a car battery charger or getting a jump from a friend's car to get it to turn over
If the radio has a security code you will have to insert the code for the radio to work.
Could be the battery is drained or bad. Could be battery connections at battery and or starter are dirty and or loose. Could be starter solenoid is bad. Could be starter is bad.
You either have a corroded or loose battery cable connection at the battery, a defective or drained battery, defective starter relay or starter.
Jump start car and do not run heater with engine not running.
You have enough battery power to power the radio, but not enough to turn over your engine. CHeck battery.
Car battery is run down.
Dead battery? Battery cables in need of cleaning or replacement?
the battery is dead
you could have left the battery disconnected. or maybe you drained the battery, you might have to recharge it
Not with out being attached to a battery charger. On a 10 amp charger in 8 hours it will charge enough to start the car, allowing the battery is god enough to charge
check if your lights are still on that drained the battery