Quick Bug fix for my website

I am using a video script from ([login to view URL]) to run a tube website. I am having a problem for my users to log into the website Here is what happened My website was inaccessible and I contacted my hosting provider, they told me that mysql was overloaded and my website was running out of disk space, so they told me that they rebooted mysql and cleared some uneccesary files like error log files and the website was back running again. After the issue was resolved, the whole website was working fine exept I was not able to logging to admin panel. when I looked into it I saw thats it was not only me but all users can not login nor register. I tried entering a wrong password to see what happens. when you enter a wrong password it does tell you you entered the wrong details, I tried password recovery and its works fine it does send you an email with your forgotten password. but when you enter the right login details instead of logging you in, the page just refreshes. My hosting provider said they can not help me with that cause its related to the website it self and they told me it should be an easy fix, its probably session issues or maybe cookies. I contacted my script provider but they usually take days to answer, I need to fix this quickly reason why I wanna hire someone that can do it for me since I am not a qualified webmaster. Thanks