I cant access the Web Interface at all

You need to find out which IP has been assigned to your NAS. You can check this in the router.

Or, if you have a keyboard and display connected, on the NAS directly. For that login with root:password and type

ip addr

Then write this address in a browser on a computer on the same network.

In my signature you find a link to the "New User Guide", which might be helpful for you.