For some reason my Ubuntu was restored to another date. All the files I have created since that date are disappeared and the files I have deleted reappeared.
I have restarted my PC many times and I could get back my files. Its really strange!
I figured the problem. I have used CloneZilla to clone my Ubuntu to another partition. Without knowing when I boot, some times I enter to the cloned partition and some time I enter to the other Ubuntu.