Check the thermostat first
Make sure it's set to Cool, the set temperature is below room temperature, and the batteries aren't dead. A blank screen is often just batteries.
Look at the air filter
A clogged filter chokes airflow and can freeze the coil. If you can't see light through it, replace it. Most homes need a new filter every 1 to 3 months.
Check the breaker and outdoor switch
The outdoor unit has its own breaker and a shutoff box near it. If either is off or tripped, reset it once. If it trips again, stop and call a pro.
Clear the outdoor unit
Leaves, grass and fences closer than about two feet block airflow. Rinse the fins gently with a hose, never a pressure washer.
When to call
Ice on the lines, a humming unit that won't start, burning smells, or water pooling indoors all need a technician. Turn the system off until then.
General information only, not legal or professional advice.