This is a common issue. Several times a year, the cable modem that your cable company supplies needs to be restarted. If you find that your internet is not working, locate your cable modem and restart it. You can restart it by simply unplugging the power cord from it, waiting 30 seconds and plugging it back in.
If this happens more then 4-5 times a year then you will need to schedule an appointment with the cable company so they can evaluate the issue.
Alternatively, we deploy specific systems that sense internet outage automatically restart your cable modem, and other network devices. This system keeps your systems online more consistently, and work in the background - never needing your input.