Changed Network Key

My wireless stopped working 2 days ago. The router is on and fine, but stopped connecting to my computer. No obvious damage was observed. When I went through the trouble shooting process, www.routerlogin.net showed me a different Network Key (password) by 1 letter, from what is on my paperwork and device (and have been using for years). It seemed fishy that the password changed on it's own.  Any advice? Thanks!