I fixed a few of these. It turned out the owner was using the USB connection to the DSL modem. Sorry I have yet to find a good cure to make that work.
If this doesn't apply to your setup, remember you didn't tell us much.
I keep having the same problem with my DSL service, but it's hard to pinpoint (which means Verizon will tell me everything looks fine).
My browser launches on startup. It almost never has problems fetching the startup page, set to My Yahoo. But then I'd often have problem getting to any website, including Yahoo, or getting email. "Repairing" the connection doesn't work (I'm on Win XP Pro), and usually I'm forced to turn off the router, and reboot the computer as well. Things usually work after that, but sometimes, and not too infrequently, the Internet connection could also terminate when I've been online for awhile, like just now as I try to post this message.
Even when I don't have to reboot, I usually have to wait half a minute or more after startup before the connection resumes working (remember the browser always fetches the first page).