The next time it does that try going to this website:
188.8.131.52 <---this is letsgopens actual web address. If you type that in and get the site you know there is a problem with your DNS lookup server.
When you type www.letsgopens.com
into your web browser, it asks your DNS server to convert that alphabetical url into an ip address. For most people their DNS server is run by their internet provider. There are some other alternatives (Google being a big one) that you can set up if you have trouble with your DNS.