Routers and modems (and router-modem combos) are essentially little computers. For the most part, they can run 24/7 without a problem, but the longer they stay on without a break, the more likely they'll develop software errors. Errors that can cause a disconnection.
It may be a cliche, but when your internet stops working, the first thing you should do is restart your equipment.
- First, unplug your router and broadband modem from power (for some devices you'll have to remove the battery as well).
- Then wait about 30 seconds, and plug them back in: first the modem, then the router.
- Wait a few minutes for them to completely power back on. If your equipment had encountered an error, the restart should fix it and your internet should be back up.
Even if you haven't encountered any errors it's a good idea to periodically restart your router and cable modem (especially the router). Once per month is a good pace. This will help keep your connection working and should reduce the possibility of losing internet at an inopportune time. Some routers make this easy with an on/off button, and some have features that allow you to program an automatic restart on a schedule.