Build an Online Store

We have a website on prestashop 1.5.6.1, which is working on a dedicated server of xeon 4 core 3.2 ghz processor and 8gb ram. This is the only site working on that server. Unfortunately the SQL hangs and we need to restart the Mysql on daily basis as to make site function smooth. following is the log Log Messages 160420 17:18:58 [Note] /usr/sbin/mysqld: ready for connections. 160420 17:18:57 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 160420 17:18:57 mysqld_safe mysqld from pid file /var/lib/mysql/[login to view URL] ended 160420 17:18:57 [Note] /usr/sbin/mysqld: Shutdown complete 160420 17:18:56 [Warning] /usr/sbin/mysqld: Forcing close of thread 800 user: 'eximstats' 160420 17:18:54 [ERROR] /usr/sbin/mysqld: Sort aborted: Server shutdown in progress 160420 17:18:54 [Note] /usr/sbin/mysqld: Normal shutdown 160420 16:51:52 [Note] /usr/sbin/mysqld: ready for connections. 160420 16:51:51 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 160420 16:51:51 mysqld_safe mysqld from pid file /var/lib/mysql/[login to view URL] ended 160420 16:51:51 [Note] /usr/sbin/mysqld: Shutdown complete 160420 16:51:50 [Warning] /usr/sbin/mysqld: Forcing close of thread 294 user: 'eximstats' 160420 16:51:50 [Warning] /usr/sbin/mysqld: Forcing close of thread 11850 user: 'leechprotect' 160420 16:51:48 [Note] /usr/sbin/mysqld: Normal shutdown 160420 16:30:01 [ERROR] /usr/sbin/mysqld: Table './buyatbra_2014/ps_customization_field_lang' is marked as crashed and last (automatic?) repair failed 160420 15:02:16 [Note] /usr/sbin/mysqld: ready for connections. 160420 15:02:14 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 160420 15:02:13 mysqld_safe mysqld from pid file /var/lib/mysql/[login to view URL] ended 160420 15:02:13 [Note] /usr/sbin/mysqld: Shutdown complete 160420 15:02:12 [Warning] /usr/sbin/mysqld: Forcing close of thread 52 user: 'eximstats' 160420 15:02:12 [Warning] /usr/sbin/mysqld: Forcing close of thread 102559 user: 'leechprotect' 160420 15:02:10 [ERROR] /usr/sbin/mysqld: Sort aborted: Server shutdown in progress 160420 15:02:09 [Note] /usr/sbin/mysqld: Normal shutdown 160420 12:30:01 [ERROR] /usr/sbin/mysqld: Table './buyatbra_2014/ps_customization_field_lang' is marked as crashed and last (automatic?) repair failed mysql restarted successfully. This site gets around 70 users at a moment, live in real time google tracking. Please share if someone can fix this issue