i get a 0.0.0.0 ip and cannot renew

since isabel, my computer hasn't been able to connect to
the internet via external cable modem, which has been
working for a year now. the connection works fine with my
roommates' computers, but mine is having very mysterious
problems. i made no changes to my computer.

my computer recognizes the modem and the connection
subsequently appears on my network connections. i get
0.0.0.0 for my ip, and when i try to /renew, the error
message says "the system cannot find the file specified".
what file??

i've been on tech support with my ISP the last few days,
we've tried all the standard approaches including 'netsh
int ip reset resetlog.txt'. i've also tried a repair
installation of XP but that didn't help either. i've tried
using both the USB and ethernet connections from the modem
to my computer.. both yielded the same error.

please help!!

thanks
miles