I deleted my.minecraft folder and downloaded 1.7.4 again. It downloaded fine. Then I downloaded 1.7.2 but it doesn't finish downloading. After the green line gets to the end, it disappears and the launcher stays there.
I tried deleting the.minecraft folder again and download 1.7.2 first and still it doesn't finish. Then I deleted the.minecraft folder again and downloaded 1.7.4 and then I asked my friend to put his 1.7.2 folder (the one in the versions folder) and I put it in my versions folder. Minecraft loaded faster this time but again it didn't finish.