[TomR]

The person who set the modem and router up would be the best person to ask.

In order to eliminate the possibility that the router is causing the problem you want to run the cable from your computer directly into the modem that the internet provider provided instead of into the router. There may be some sign in information that you will need in order to plug your computer into the modem.

If the person who set this up is not available we may be able to help you, kinda doubtful, but you haven't provided some important information:
Who is the internet service provider?
Who has the account with the internet provider (they will have the sign in information that you may need)?
Do you have access to the modem?