You need to learn to reflash, so focus on that. Follow the instructions carefully, especially the one about holding down the button on the front left of your N810 (not on the screen; it looks to me like a square white rectangle).

As you turn on your N810, keep holding that button down till you see the usb symbol appear on the upper right corner of the screen. Then is the time to release the button you have been holding down.

Once you have gotten this far, continue to follow the instructions on the screen and you will probably flash easily.

This is actually an easy process; it's just hard till you learn how to do it. Following the instructions that come with the flashing software is the key.