can not connect internet with dlink

I bought a mac air and try to connect to internet. I have Dlink DSL2740B modem+router. When I try to connect with mac it says internet connection fails. And after that the internet connections of all the other pcs fail and I have to set up the router again. I have a pppoe bridge connection and using WAP security. Mac air does not have an ethernet port,will it help connecting via ethernet to the router, or what else should I do?

Try setting security to WPA2.

It seems odd that an attempt by the Mac to connect would cause problems with the router. Check the router logs to see if something weird is going on since this sounds like a router issue more than anything else.