Some ISPs don't allow just any router, it has to be one of their own.. so, that suggestion may not work... but viability should be a phone call away.
I would be suggested doing this:
1. Reset the router by either;
a) resetting it by pushing a paper clip into the pinsize reset hole, or
b) removing the power wire for 10 seconds.
2. If you have trouble accessing the Internet or the router settings afterwards;
a) if you still have the box the router came in, it should have the default user and password on a label, or ask the ISP for such information.
b) if you have trouble accessing the router settings through 192.168.0.1, the settings default user and password should be available online searching with router brand and model.
3. If all that fails, you can always call the ISP to ask for the passwords.