Domain/Local Security Policy

I implemented a domain secuity policy to prevent users from logging in interactively on any system on my network and it worked fine. I changed this policy back to what it was ie allow users to log in interactively. All the systems on the network complied but one. Now this system that has refused to comply is my application server and has denied everbody including the administrator access to it. I do not want to reinstall the operating system as this will result to a downtime. Please I need advice on what to do to gain access to this computer.