Have you tried to reset the belkin router? This may require you to power it off first, then holding the reset button in, powering it back on and keeping the reset button pressed for 10 seconds or so. The exact instructions for the reset should be in the manual.
Also, I don't want to leave the NIC on the computer out of this problem either. After all, the modem works......it appears that the functionality of the router to, at least, obtain an external IP address is working fine, how about taking a straight-through CAT5 cable from the DSL modem to the PC? Can you access the internet (without USB) from the PC in question thourgh just the cable modem? As the sencond solution may take a little bit to setup....try resetting the router first.
-Mike