Let's see now..
- The internet is OK, but your sister is clueless
- No internet connection because she didn't pay the bill and the ISP cut the service
- No internet connection because the modem is broken
- No internet connection because the cable between the modem and router is broken
- No internet connection because the router is broken
- No internet connection because the router is misconfigured
- No internet connection because the wireless adapter is broken
- No internet connection because the wireless adapter is misconfigured
- No internet connection because the operating system is broken
- No internet connection because the operating system is misconfigured
- No internet connection because the browser is broken
- No internet connection because the browser is misconfigured
And these are just for starters
Maybe you should provide some more information here..