alot of users showing as guests?
 

on there posts they cannot login and shows

for the post he did... anyone help me plz?

It sounds like the users have been deleted from the database. But, I probably couldn't help with why. I just know that's exactly what happens when you delete a user. Can you find the users in your AdminCP? Do you have other admins? Is it possible that somebody deleted them on purpose? Have you checked your admin log? Have you been having database problems?

That doesn't sound good, I hope somebody else has a better answer :D

hmmm ill have to look into it, i know its not my admins my forums is kinda dead, trying to get it active again and they havent been on for a long time lolz, but yeah it shows them as guests on there posts and i cant edit them in admin cp because there gone, only way for me to remove them is removing the whole post.

I'd check your Admin CP Logs and see if some script ran that deleted inactive users or something like that.