Firstly, why are you using the 3rd-party software that was supplied with the adapter?! Not necessary and not generally a good idea, except for 9x users. That said, your specific issue is 80/20 either way (probably the router, may be the adapter) but you're not doing yourself any favours by using that software.
Secondly, *which* Belkin router? I need to know in order to check through my growing collection of manuals and tell you how to check the default gateway. The chances are good that it's slightly different to mine.