Open Internet Explorer.
You can find this by searching using the magnifying tool.
Open Settings by clicking on the cog wheel in the upper right corner.
Then, click on Internet Options.
In the pop up box, choose the Security tab.
Then, click on Custom level.
In the Security Settings dialog box, scroll down until you see the User Authentication settings section.
Select Automatic logon with current username and password.
Click OK.
On the Internet Options tab, click OK.
Then, close Internet Explorer.
You should no longer see the SharePoint login credentials box pop up.