Can you find history of time computer was shut down/turned on?

Your system.log files will show start/stop times along with other information. To view the files run Console.app located in Applications>Utilities>Console. Select the "Logs" icon and the log files are shown to the left.

Regards,

The command "last username" can be used to find the most recent login times for a given username, and goes further back in time than system.log. The user reboot "logs in" each time the machine is booted, and the user shutdown "logs in" each time the system shuts down or (including a reboot). There's no easy way to find when a machine has shut down due to forces beyond the system itself (i.e., a power failure will not log a shutdown).