MacBook Air Not Powering on but charging

Sounds like a liquid damaged keyboard, is the magsafe charger light always switching to green momentarily when you hit the power button and have the magsafe charger plugged in?

If yes I strongly recommend getting the MacBook inspected on the inside for signs of liquid damage / corrosion. The earlier it’s treated the better the outcome will be for liquid damage repair, sometimes if it’s not severe enough a keyboard replacement and some isopropyl alcohol cleaning with cotton buds will fix it.