Hi Ive just downloaded the magic launcher, but when I enter my username and password (entering email address) it says incorrect details. But when I log into my mojang account, its right. Any ideas?
Though best results for Minecraft is with the default launcher, sometimes people have a personal preference for something that best fits their style.
I'm not overly familiar with Magic Launcher because of the aforementioned but because it's not a cracked launcher, generally trusted by ethical players. Unfortunately there is no official site for this application so I wasn't able to direct you to any official support, however, the swath of support and tutorials for troubleshooting problems is wide with some even appearing on Minecraftforum.net and MinecraftSix, two places it can be obtained directly and are trusted among ethical players.
I did find a YouTube video that specifically addresses the problem you're asking about.