How to Tell the Last Time a Computer Was Rebooted
The Task Manager applet in Windows 7 and Windows 8/8.1 provides detailed feedback about your computer’s hardware components, including how long your computer's been up and running. The Command Prompt console can also provide other information, such as the exact time and date that your computer was last turned on. You can use this information to schedule future updates and manage downtime periods for maintenance, or even to determine whether someone has tampered with your computer while you were away.
Checking Computer Uptime
Right-click anywhere within the taskbar and select “Task Manager” to open your computer’s Task Manager applet. If using Windows 8/8.1, click “More Details” to expand the window. Under the Performance tab, check "Uptime" to find out long your computer’s been on; in Windows 8/8.1, click “CPU” to see your computer’s uptime. Alternately, to find out the exact time your computer was last turned, press “Windows-R,” type “CMD” (without quotes), and then click “OK." Type the following command into the Command Prompt console, and then press “Enter” to get the information:systeminfo|find "Time:"