LAN ethernet card AND wireless card will not connect to the internet, what

[mysticaria]

hardware is broken? This is definitely a hardware issue, a few people have already looked at the computer and there is no problem with the settings, IP, router, and the network card diagnostic says its running fine. This is a new system from DELL and only 5 months old running on VISTA. Internet started cutting in and out for a week and then internet connection stopped entirely. Does this mean both cards could be working and there is another hardware problem that won't let them connect to the internet? It would be odd if BOTH cards failed at the same time! The wireless card detects networks at full strength, but then when you try to connect it says it can't connect to the internet because it can't communicate with the router. When you plug a working internet connection into the LAN, it says Limited Connectivity briefly and then just turns into the X for nothing plugged in.
I have already tried this system on three different internet connections, routers ,modems work fine, just both my cards stopped functioning.