You say that:
>>> When ever I try to connect using my lap-top via
>>> a wireless connection, I simply get a message
>>> saying it was unable to connect to the internet.
Presumably the computer located downstairs has a "wired" ethernet connection to the router? If this is the case, is it getting online OK via the router?
The answer to that will determine whether the problem is with the "Laptop to Router" wireless connection or the "Router to ISP" connection.
If it turns out to be a "Router to ISP" problem, I'd suggest hard resetting the router back to factory default settings, but this would involve configuring it again from scratch so you would have to know how to do that.