Login Problem

Hello everybody in house please I am having problem with my wordpress site. I created a plugin for it but the plugin runs fine initially but all of a sudden it stopped working. It stopped working in the sense that users cant login into their account again, and I am losing money with this problem. please help!!!!!!!! the site is at https://www.lagsms.com its a bulk sms portal where members can send text messages to their phone from the internet.