Summarize this article:

These two antivirus programs have been known to cause the most problems with browsing websites. If you have one of these antivirus programs installed, consider removing it and replacing it with a lightweight, unintrusive antivirus.  See Uninstall Norton Internet Security for instructions on completely removing Norton software, which can be tricky. See Uninstall McAfee Total Protection for a guide on removing McAfee Security Center, another difficult program to get rid of. After removing the old antivirus, you'll want to make sure that you have a new program installed to protect your computer. See Install an Antivirus for general instructions on installing a new antivirus. The following free antivirus programs are highly-rated by security professionals and should not get in the way of loading websites:  Avast! BitDefender AntiVir Microsoft Windows Defender Having multiple antivirus programs installed at the same time can cause problems. Conflicting protection could lead to some websites not loading. Keep the antivirus program that you like best and get rid of the rest. See Uninstall a Program for general instructions on removing programs. You can also find uninstallation guides for most popular antivirus programs on wikiHow.

Summary:
Uninstall Norton or McAfee. Install a lightweight antivirus to replace your old one. Ensure you only have one antivirus program installed.