Too many “extensions” bogged it down. Extensions let you launch games, music, chats, etc. right in your browser, but they also slow your computer. They accumulate faster than you realize and sort of sneak up on you. To see your extensions, click the icon of a wrench in Chrome and choose “settings.” Then click “Extensions” and the whole list comes up. Click to disable the ones you don’t want.
Duplicate plug-ins can also cause problems. Type “About:plugins” in your address bar in Chrome to see if you have duplicates of “Adobe Flash,” for example, a common over-loader. Disable the duplicate that’s located in your “users” folder and leave the one in the Windows folder.