Thanks for the tips, but the problem is still there.
I checked, and all the files have been copied.
The problem is that I uploaded the 2.8.3 without having turned off the widgets and plugins.
Now i copied again the default_widgets.php
And since the problem should be with the widgets i deleted the old widget.php and replaced for the one with the 2.8.3
now the errors appear like these:
Warning: wp_maybe_load_widgets() [function.wp-maybe-load-widgets]: Unable to access /home/t44241/public_html/wp-includes/default-widgets.php in /home/t44241/public_html/wp-includes/functions.php on line 2728
Warning: wp_maybe_load_widgets(/home/t44241/public_html/wp-includes/default-widgets.php) [function.wp-maybe-load-widgets]: failed to open stream: No such file or directory in /home/t44241/public_html/wp-includes/functions.php on line 2728
Fatal error: wp_maybe_load_widgets() [function.require]: Failed opening required ‘/home/t44241/public_html/wp-includes/default-widgets.php’ (include_path=’/usr/lib/php:.:/usr/php4/lib/php:/usr/local/php4/lib/php’) in /home/t44241/public_html/wp-includes/functions.php on line 2728
What can I do now?