Clean up my registration system.

I have a login script which i am using on a project, over time, new fields have been added to the login system, and recently i had it overhauled by a freelancer. However since then it has had issues, new fields have also been added since this time. And it seems to fail regularly. The login system is being used for a job board project and i think the system fails when users try to use apostraphies, back slashes and other items which will be considered threatening all though it is important that the user can use these elements in their profile, without making the system vulnerable. What i need is for somebody to work through the code, and clean it up, ensure that it is free from any vulnerabilties and that it works perfectly fine. The most important thing, which it doesn't do at the moment is if it fails it emails an email address and tells us why a user was unable to register and what the problem was or at least what section of the registration process caused the problem. I have attached our code for you to look at, this doesn't include the register page, just the code. All the information collected on the register page is passed to process.php.