If the MX is powered up and plugged into nothing else but power and your notebook, you should be able to get to:
http://mx.meraki.com
If this is not the case then I suspect the factory reset has not worked properly.
Another option is to create a temporary network and move the MX84 there. You will get a licence warning, but it will be fine for up to 30 days.
Then plug the WAN port of the MX into your existing LAN, and let the unit come online and try and sort itself out.
Then try accessing the local status page again,