How do I unblock a website

I use the website of a well-known grocery chain to access my account with them. For a couple of weeks I've been getting a message saying the website operators are "aware of the problem and it will be fixed shortly." Today I asked my husband to try on his computer and he got thru with no problem using the same web address. We are both using Windows 7 but he uses Firefox and I use IE. We both use Norton 360. I suspect that somehow I have put a block on this site or that my Norton 360 might have done it.  How do I check to see what sites are blocked on my computer and then, how do I unblock? 

 

Just to be clear: no warning from N360.