pull out battery, press the power button 3 seconds, then just put the battery back in and turn it on
It may happen that your rootfs is full of log file because ksyslogd doesn't use logrotate out-of-box and also logrotate isn't really needed but I never didn't managed myself to get ksyslogd logrotate without using logrotate. I'm not sure how you can verify if rootfs is full.