If you're having trouble loading Pins on Pinterest or logging on to Pinterest, please check to see if you use the Avast! browser extension, as it seems to be interfering with Pinterest. Most Pinners have been able to use Pinterest after disabling this extension!
On Chrome, to disable your browser extensions, on your browser toolbar, click on 'Window', then 'Extensions' and you should see an option to do so.
Here's how you disable add-ons in Firefox: Disable or remove add-ons
Also, if you'd like, you can click on the browser extension and select 'Social networks allowed'.