Okay, first thank you for choosing my post to help you:) Just follow these steps and you'll be able to sign in to your account in no time.
Step 1: Go to Xbox Home.
Step 2: Go all the way to the right to the Settings tab.
Step 3: Select System, Select Storage, Select Hard Drive, then Select Profiles.
Step 4: Find your profile and delete it. Make sure to select PROFILE ONLY. If you don't do this, then it will delete anything on your console that belongs to your gamertag.
Step 5: Go back to where is shows Hard Drive and Cloud Storage. Highlight Hard Drive with the green selection bar.
Step 6: Press Y on your controller. Now select Clear System Cache, then Yes.
Step 7: Go back to Xbox Home.
Step 8: Restart your console. (Turn it off, then back on.)
Step 9: Download your profile, make sure to select Remember Password.
I hope this really helped you. If you completed the steps, you should never see this problem again. Have a great day:D