How to find out uptime on Windows?

• Run command line
• Type Systeminfo

• Find "System Boot Time"

  Days: 10 Hours: 10 Minutes: 10 Seconds: 10

For shorter result you can use:

systeminfo | find "Boot Time" 

there is great command line tool from Microsoft uptime.exe:

http://www.microsoft.com/downloads/details.aspx?FamilyID=BC18FFDB-D6FE-400B-B892-94783AE44C91&displaylang=en

good thing with this tool is it works really fast.

Uptime [server] [/s ] [/a] [/d:mm/dd/yyyy | /p:n] [/heartbeat] [/? | /help]
server Name or IP address of remote server to process.
/s Display key system events and statistics.
/a Display application failure events (assumes /s).
/d: Only calculate for events after mm/dd/yyyy.
/p: Only calculate for events in the previous n days.
/heartbeat Turn on/off the system's heartbeat
/? Basic usage.
/help Additional usage information.

Open the command prompt and type:

net stats srv | find "Statistics"

Example output:

>net stats srv | find "Statistics"
Server Statistics for \\4IFS-SANDER
Statistics since 22/07/2009 10:14:14

Source (MS KB).

Edit: Actually this will tell you the date and time when the pc was up from, not the duration.