There are two common reasons for this:
1. Issues with your computer.
2. Issues with the Pinterest servers.
In case of computer issues you can try the following steps to correct the issue:
- A hard refresh using CTRL+F5
- Clear the cookies and cache on your browser
- Try a different browser (we recommend Chrome or Firefox.)
In case of issues with the Pinterest servers, and in the event of the above solutions not working, you may simply have to wait until the problem corrects itself.
A good way to tell whether it's a sitewide server issue is by looking on Twitter or Facebook at updates using the #Pinterest hashtag. If there are issues, people, pages and sites will be messaging about it.