Leaving off mains will result in a the system going through a couple of reboots when next powered-up perhaps as though the CMOS settings have been lost.
When off mains the systems RTC Real Time Clock will freeze and will show the time & date in Windows when last running. The system will synchronize after another reboot but the Sync function within Windows will fail with a Time Server related error.
The original installation has a McAffee Web Advisor app installed. This might have interferred with Time synchonisation [?]