Plugging in a monitor and watch the boot messages of the raspi is a very good idea. Additionally or even alternatively you could take a look at your routers Wireless or DHCP screen (or whatever it's called for your router) and try to identify, which entry appears only after you plugged in / booted your raspi. You'll find the IP spelled out there.
Check where it is listed, some people end up with their raspi listed with the Guest Network
while all the other device are on the local network. That's a possible source of problems.