How to find Windows uptime (How long since the computer was turned on or re-started) depends on the version of Windows that you are using:
Windows XP:
1. Go to “Start” -> “Run“.
2. Write “CMD” and press on “Enter” key.
3. Write the command “net statistics server” and press on “Enter” key. ( The command “net stats srv” can be use instead.)
4. The line that start with “Statistics since …” provides the time that the server was up from.
Uptime.exe Tool Allows You to Estimate Server Availability with Windows NT 4.0 SP4 or Higher. http://support.microsoft.com/kb/232243
Source: http://support.microsoft.com/kb/555737
Windows 7:
- Right click on Task bar, select Task Manager or press Ctrl+Shift+Esc
- Click the “Performance” tab.
- Uptime will be listed in the System statistics.
Source: http://www.addictivetips.com/windows-tips/check-windows-7-uptime/