Hello,
it seems that somethings wrong with your log, obviously.
With the following commands you could clear the log and hopefully the DB will start again.
But if you do this, be aware that you will lose data!
dbmcli -d <SID> -u control,<xxx>
>db_admin
>db_connect
>db_execute clear log
>db_offline
>db_online
Regards,
Michael