Please check the screenshot.
Anyone having any idea about this please reply asap.
Thanks in advance!
Something must have been changed on the server, are you trying to make some change such as an upgrade?
Can you give us some details about the server, for example: Moodle version, server operating system and PHP version.
The error suggests that the blocks folder is missing or is empty. Each block listed in your screenshot should correspond to a subfolder in the blocks folder with the same name:
$ cd /PATH/TO/moodle/blocks
activity_modules course_list mnet_hosts search_forums
admin_bookmarks course_overview moodleblock.class.php section_links
badges course_summary myprofile selfcompletion
blog_menu edit_form.php navigation settings
blog_recent feedback news_items site_main_menu
blog_tags glossary_random online_users social_activities
calendar_month html participants tag_flickr
calendar_upcoming index.html private_files tags
comments login quiz_results tag_youtube
community mentees recent_activity tests
completionstatus messages rss_client upgrade.txt
Are these subfolders present on the server?
I should add that support for Moodle 2.8 ended nearly five years ago. Also Moodle 2.8.3 is missing fixes from the final update, 2.8.12, including 51 security updates.