Okay i sent you an email throught contact form.
Thanks

Are you using sh404SEF or another SEF extension?

I use sh404SEF . You were able to find out whats the problem ?

It is related to sh404sef.
Check your overrides to see if the itemform.php file is the same as this -> github.com/joomlaworks/k2/blob/master/components/com_k2/templates/default/itemform.php#L396

If the issue persists, and sh404sef keeps changing these links, you need to address this issue to the sh404sef devs.

The file was same as the one on link you gave me.
But i fixed the problem.
I will tell you how so you can know for the future if anyone have the same problem as me so you can tell him what to do.
These are the steps:

I took the link from the following line 396:
<div class="panel" id="Remote_video"> <a id="k2MediaBrowseServer" href="index.php?option=com_k2&view=media&type=video&tmpl=component&fieldID=remoteVideo"><?php echo JText::_('K2_BROWSE_VIDEOS_ON_SERVER')?></a> <?php echo JText::_('K2_OR'); ?> <?php echo JText::_('K2_PASTE_REMOTE_VIDEO_URL'); ?>
and just made the new SEF URL.
So what i did was simple:
Logged in into my joomla administrator ->Components->sh404SEF->Url manager-> then in the left top corner i clicked on New ( for making new url ) and there i put the following:
New SEF URL: video-media
non-SEF url: index.php?option=com_k2&view=media&type=video&tmpl=component&fieldID=remoteVideo
After that i changed the "index.php?option=com_k2&view=media&type=video&tmpl=component&fieldID=remoteVideo" in the line 396 to be "video-media" and uploaded itemform.php back on the ftp server.

So my line 396 now looks like this:
<div class="panel" id="Remote_video"> <a id="k2MediaBrowseServer" href="video-media"><?php echo JText:<div class="panel" id="Remote_video"> <a id="k2MediaBrowseServer" href="video-media"><?php echo JText::_('K2_BROWSE_VIDEOS_ON_SERVER')?></a> <?php echo JText::_('K2_OR'); ?> <?php echo JText::_('K2_PASTE_REMOTE_VIDEO_URL'); ?>

And that was all.
Now it works all fine. Video upload works and Media browse throught All videos works fine.
Thank god i solved this, this was a headache for more then a month for me :)
Thanks Krikor for help and hope this what i wrote will help you and save you from future bothering and wasting time! :)

Marko I am glad you solved this.

The solution you sent me will definitely help a lot of users (and me of course) :).

Cheers