If you are using Google chrome on your PC, then update (currently v 55) to the latest version of the Google chrome browser as soon as possible. Otherwise you can’t access the “Standard View” of the Gmail as well as you will not have access to new features and bug fixes of the Gmail.
Recently the tech giant published a blog about the support to the Gmail on Chrome Browser. In the post they clearly mention that if you are using a backdated version of the google chrome browser v53 or below then your Gmail account will be more vulnerable to security risks. Also you cannot access the new features and bug fixes. But you can access Gmail on a backdated chrome browser but it will be redirected to the HTML View of the Gmail as early as December 2017.
In the blog they also said that the user of the Windows XP and Windows Vista operating system are mostly affected. Because the Google Chrome v49 was the last version for these two operating systems. Microsoft also announced in 2015, they are not providing any support to Windows XP & Windows Vista after April 2015 & November 2015.
So if you are using Windows XP and Windows Vista, then upgrade your operating System to a secure and supported OS. Otherwise you have to update your chrome browser to the latest version to access your Gmail account more securely with new features and bug fixes.