Can't REdownload already purchased song

I have two songs I have purchased in Itunes. They did download at the time and are still listed in my library. Now neither can be' found' when I try to drag them to make a CD. No idea why. Its happened before. I get that frustrating exclamation mark!

They are listed in my purchased account but the download option next to them is greyed out -so can't download again. It's the SAME laptop. Only bought the songs 2 weeks ago. I dont have any other Mac products like iphones etc. How can I get the songs I paid for please.