This happened due to user profile corruption. By editing/renaming your S-15 folder in Windows Registry can fix this issue. For the step by step process watch this troubleshooting video http://www.youtube.com/watch?v=X2REmXBrMLU
You need to login as admin and manage all the other user accounts from there.
If you can't login as admin there's nothing we can help you with on this forum. We don't provide security bypassing solutions.
This happened due to user profile corruption. By editing/renaming your S-15 folder in Windows Registry can fix this issue. For the step by step process watch this troubleshooting video http://www.youtube.com/watch?v=X2REmXBrMLU