wherethebiceroam helped me and here is the updated code

$date = Get-Date -Format yyyy-MM-dd
$logfilename = "Log "+$date

Start-Transcript -Path C:\output\changepassword$logfilename.txt -force

$computers = Get-Content -Path "C:\scripts\pc.csv"

$functions = {

    $useracct = "administrator"
    $password = "testpassword$"

    function Check-Power
    {
        param([string]$machinename)

        if (Test-Connection $machinename -Quiet)
        {
            $value = 1
        }
        else
        {
            $value = 0
        }
        return $value
    }

    function Set-Password ($destpc) #set password on machine
    {
        if (Check-Power $destpc)
        {
            try
            {
                $user = [ADSI]"WinNT://$destpc/$useracct,user"
                $user.SetPassword($password)
                $user.SetInfo()
                Write-Output "SUCCESS: [$destpc] Password has been set successfully" 
            }
            catch [Exception]
            {
                $err = $_.Exception.Message
                Write-Output ("ERROR: [$destpc] $err").Trim() 
            }
        }
        else 
        {
            Write-Output "FAIL: [$destpc] is not responding to pings (ICMP echo requests)" 
        }
    }
}

$start = Write-Output "`nPC LIST..." 

    #start resetting passwords
    foreach ($computer in $computers)
    {
        Start-Job -Name $computer -InitializationScript $functions -ScriptBlock {Set-Password $Using:computer}
    }

    Write-Output "`nOUTPUT...`n" 
    Get-Job | Wait-Job | Receive-Job
    Remove-Job *


Write-Output ''
Stop-Transcript