404 Page Not Found

Every new post I make comes up as 404 Page Not Found when I look at my blog. The post shows on my home page but when you click on it to read the whole blog you get the 404 message. I’m just starting out so maybe I’ve made some simple error but when I did my first few posts yesterday this wasn’t happening. When it did start to happen I deleted all my posts and started again but still the same problem. Any suggestions??

Ross