I've had issues in the past with my Internet going out for extended periods of time. After dealing with my service provider for the first few times, I take care of the problem myself if it happens now.
The first thing I usually check is my router and wireless access point. Cycling the power on these is usually my first step. After they come back up (usually within 2 minutes) I check my Internet again. If there is still no Internet, I reset my cable modem. Since my modem also runs my digital phone service, it has a battery backup in it. To reset it, there is a reset pin-hole button on the back of the modem. Using a paperclip, I hold the reset button for 30 seconds until all of the lights on the modem go out, then release.
It takes about 5 minutes for the modem to come back up completely.
Usually after these steps, I have Internet again. If I don't, I call my service provider. At this point, it usually boils down to either an area-wide outage, or a damaged wire.
Hope this helps!