Well, that's the "normal" way to boot things up.
The modem boots, connects to the ISP, and requests an IP address, then accepts
local connections. The router connects to the modem, doing basically the same thing.
Your computer then connects to the router, and winds up on the end of the chain.
If for some reason your modem or router loses power, or gets rebooted, or you just
don't want to be "normal", click Start, Run..., then type WINIPCFG , then click OK.
When tht IP Configuration box pops up, you'll probably see PPP Adapter listed first.
Use the drop-down list to select your ethernet card (usually the one that makes the
Release and Renew buttons clickable). Click Release, wait a few seconds, click Renew,
wait several more seconds, and you should be connected again.