Hey Natalia—
Let’s see what’s going on here. First, could I get your EE2.x version and build number? See EEWiki:// HowTo Determine My EE Version
Looks like you have more than one channel on this site and all the others work as expected, but this particular one won’t allow new posts, correct? Are there any new fields that have been added to this channel since it last worked as expected?
When the publish page reloads on submit, does it present any kind of message? Success, error, or otherwise? After you click submit, does the publish page come back with the old entry content?
Try disabling your extensions and then trying to post again. It could be that an extension is interfering with the publish page submission, so let’s disable all of them first to see if that narrows it down. See EEWiki:// HowTo Disable Extensions via the Control Panel
I’m keeping an eye on this thread. Let me know what you find!
Kevin