I have an Inspiron 15R 5521 that would not power on. I replaced the motherboard and still the same issue. I happened to turn to try to turn it on without the keyboard connected and everything works fine. It only wants to charge and turn on when the keyboard is dsiconnected.
Has anyone seen this before? Could the keyboard really be the whole problem?
If still under warranty contact Dell. If not, you can buy a new keyboard from Dell or a third party (check eBay) and replace the keyboard.
It could be a keyboard controller failure. As advised by KirkD, the keyboard might require replacing.
If the system is under warranty, then please send me the service tag of the system and your contact details through a private conversation. Or you could use Twitter - @dellcares - for faster communication.
Keep us updated.