"Optimize disk" function not working

My laptop's very new - a month or two old - and is starting to slow down a bit, so I thought I'd go through the various "performance" fixes provided by my Norton subscription.  

Next to "last optimization", it says "not available" - it was my assumption that this was because I've never "optimized" on this computer before. So I started the process, and after 4 hours it still said "analyzing".  I canceled it and started it again.  I left it going overnight.  Just under 13 hours later, it still said "analyzing".  

What's going wrong?