What should I check first if my MacBook Air won't charge?

Regarding the MacBook Air: Check the charging port for lint or debris first. Use a toothpick or soft brush to clean it out — 9 times out of 10, that fixes it. If the port is clean, try a different cable and charger, as Apple’s cables die often. For Intel models, reset the SMC; for M-series, force restart by holding the power button for 10 seconds.