Remove all things you can like battery, SIM, memory card and let it sit for a minute. Then slip in the battery (no SIM or memory card) apply the charger, wait about 10 minutes to get some charge and then try again.
Sometimes that does it, if not back to your carrier counter to let them try.
My Samsung A7 mobile phone won't switch on. Only potential reason I can think of behind this would be the fact that I spilled some water on it earlier. Yesterday the phone shut down when I was charging it and refused to be switched back on but once I removed the charger I could switch it on. Today, however, I plugged the charger in again and now it refuses to switch on completely (even after I removed the charger). I tried the "press power button and volume up/down button at the same time" as well "press power button, volume up/down button and home screen button". None of them have worked. Please help ASAP. I am desperate.