With the information you have provided it would appear you have a home network and are having some difficulty with your wireless connections.
How long have you had your system up? How many computers on your local network? And have you been having this trouble since you started with your local Internet provider? And are you using DSL, cable or some other type of broadband?
There is no special reason to pick on Buffalo routers. They are as good as the rest.
You did not say what brand of wireless adapters you are using. The cheap ones are real lousy. So have you tried a different brand of wireless adapter and have you tried it on a different computer?
As for your modem, that depends whole lot on your local service provider. Some of the stuff that AT&T has put out a year ago was real junk. But by now they should have that under control.
Please supply more details. And especially let us know if you can connect from your computer to the modem without using any other hardware.