Posts Disappearing!

Hi!
This problem started after I messed up with the file permissions in my public html folder.
Whenever I add a post it appears on my website but after a hour or 2 it disappears and when I edit the post it says “The item you are editing does not exists or is deleted” but again after a hour it appears just as posted before. I dont know what is happening I have reinstalled wordpress but still the problem is not solved. I think I have to again assign permissions to file but I cant remember what to assign. Currently I have assigned 644 to files,755 to folders. Are they correct? If not please tell me so I can edit them.