wow i thought those things were pretty foolproof but you found a way. there is absolutely no way that you can get into the router from that computer now as every time you would try you would get your own computer instead.
If you cant log in using a different computer ( and you would probably have to disconect the first computer from the network also ) what you need to do is reset the router
luckily that is not that difficult to do.
on the back of the router near the power cord is a little button that says reset. It may be inside a very small hole so that you have to use a paper clip to push it in.
With the router turned on push that button and hold it for 20 seconds until the lights all flash and the router restarts
That will put the router back to factory defaults and you can log in and reprogram it again.
It is not a website. It is the programming for the router. You need to be conected to the router via ethernet cable. Reboot the computer if you have not already
then try logging in using the ip address
Did you change that mac setting in the router or in your mac ? If you changed it in the mac you need to change it in the same place
you can try the following ip address to put in your internet explorer address bar
192.168.0.1 188.8.131.52 192.168.15.1
one of those will get you a login screen 99 % of the time
default id / password are usually one of these
admin / blank ( nothing )
admin / admin
blank ( nothing ) / admin