Windows uptime

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.

4.  The line that start with "Statistics since …" provides the time that the server was up from.

The command "net stats srv" can be use instead.

Taken from: http://support.microsoft.com/kb/555737

Other possibility: the command systeminfo

And another: net statistics workstation.