Disqus is incorrectly located on the page
Most often, the best default position for the Disqus widget is in the bottom slot of the bottom-most right column.
Comment counts are missing
If comment counts were appearing on your blog but have disappeared, most likely your Blogger Layout > Blog Posts widget has become corrupted. To fix this, try the following solutions, in order:
Solution 1: Reset the corrupted Blog posts widget
This can be fixed by following Blogger's How to reset corrupted Blogger Blog Posts template guide.
Solution 2: Revert all widget templates to default
If the above guide doesn't work (e.g., if it errors out or if the comment counts still don't appear) you'll need to revert your widget templates to their default status. To do so:
Go to Blogger > Template > Edit HTML tab.
Click the "Revert widget templates to default" link.
Click OK in the confirmation message.
Synced Comments Showing Site Owner Name Instead of Commenter Name
If your blog's settings allow only certain people to comment within Blogger, all comments synced from Disqus will be shown as authored by the blog owner instead of the commenter.
To prevent this, go to Blogger → Settings → Comments and set the Who Can Comment? option to Anyone.
The Disqus gadget installer isn't working for my blog
If the gadget installer isn't working for your site, you have the option of manually installing Disqus. If you're using a standard Blogger template, see Manually adding a Disqus gadget to Blogger
Note that Blogger's new Dynamic Views templates don't support gadgets or custom HTML, so these templates can't use Disqus on them.
I've installed Disqus but Google+ comments are still showing
When Google+ comments are enabled, Disqus cannot load. You will need to disable G+ comments before Disqus will appear in Blogger – from your Blogger dashboard, click the "Google+" tab and unselect the "Use Google+ Comments" option.