If you’re connecting wirelessly, then the location may be the problem. The signal is not necessarily strong in all corners of your home or the building you’re in. Similarly, you could just be too far away from the router.
You might also need to clear the temporary internet files and reboot your computer. For instructions on how to clear your temporary internet files on a Windows computer, click here. For a Google Chromebook, click here. For a Macbook, click here.