If you have been modding recently or doing anything with your profile while connected to a PC there is a chance something could go wrong.

If your profile is corrupt when you try to open it in profile editor it will Say:Error Loading Profile:Acception!

Sometimes your gamertag will start to glitch such as not showing your gamer score or saying your signed out when you signed in or your name not showing up on the the profile list and then if you try to recover your gamertag it will say "Not enough space on hard drive to download gamertag please ensure HDD is inserted correctly here is 2 Ways to fix this:

Do not try to fix your profile on a computer you can mess things up!

Method 1:
Step 1
If you cannot recover your gamertag your gamer profile is Hiddenly Corrupt meaning you profile is corrupt but does not show the yellow yield sign. Just go to memory then profiles and select your profile and select delete then select "Delete Profile Only" if you select the other one "Delete profile and items" all your game saves and data will be erased such as halo 3 films and other game data.
After That you MUST Clear your cache!
Then after that you should recover just fine if all went well!

Method 2
This method is for if all else fails and you accidentally deleted your corrupt profile while hooked up to your computer.
Go to Xbox Dashboard scroll over to settings then go to memory and instead of clicking the hard drive just highlight it and press the "Y" Button then select "Format Hard Drive"..
****Warning***** Method to will reset your HDD and delete EVERYTHING On It this should only be used as a last resort to fix your profile. Both methods are tested and working!