Here is a PowerShell script that will prompt you for a computer name and it will output the uptime.
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#
# NAME: Get Computer Uptime
#
# AUTHOR: randolph.brady
#
# COMMENT:
#
# VERSION HISTORY:
# 1.0 1/23/2012 – Initial release
#
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$computer = read-host "Please type in computer name you would like to check uptime on"
$lastboottime = (Get-WmiObject -Class Win32_OperatingSystem -computername $computer).LastBootUpTime
$sysuptime = (Get-Date) – [System.Management.ManagementDateTimeconverter]::ToDateTime($lastboottime)
Write-Host "$computer has been up for: " $sysuptime.days "days" $sysuptime.hours "hours" $sysuptime.minutes "minutes" $sysuptime.seconds "seconds"
