My WhatsApp on my Nokia Lumia 630 is constantly not working after a few minutes. Messages are coming through but I can't access them. I've uninstalled the app over a dozen times but the same problems still persist. I deleted my history and still nothing.
Check that whether Whatsapp stopped working after an update (you can check it in downloads history). If this is the case, then, the maximum chances are this version is not supported by your phone (happened with one of my friend).
I would suggest to wait for the new version and get it updated.
If you have tried uninstalling and reinstalling the application, but the problem still persists, then I advise that you unistall WhatsApp and do a soft reset.
Whilst your phone is on:
Press and hold the Volume Down and Power buttons at the same time until you feel a vibration (about 10–15 seconds). Ignore the "slide down to power off" screen.
This method will not remove anything at all from your phone and is completely safe to attempt in any problem situation.
After soft resetting, download and install WhatsApp again from the store. It should work fine.