Monitoring servers is an important thing, almost uptime of all servers.  You should have some dedicated tools such as Zabbix, Nagios, etc… BUT ! Here is a script to generate an HTML report of all your servers uptime.

Those servers are all registered into AD and the ‘get’ is based on the operating system detected by AD.

#Function

#Get-Update - Return lastboottime and update - input : servername
Function Get-Uptime { 
    [CmdletBinding()] 
    param ( 
        [Parameter(Mandatory=$false, 
                        Position=0, 
                        ValueFromPipeline=$true, 
                        ValueFromPipelineByPropertyName=$true)] 
        [Alias("Name")] 
        [string[]]$ComputerName=$env:COMPUTERNAME, 
        $Credential = [System.Management.Automation.PSCredential]::Empty 
        ) 
 
    begin{} 
 
    #Need to verify that the hostname is valid in DNS 
    process { 
        foreach ($Computer in $ComputerName) { 
            try { 
                $hostdns = [System.Net.DNS]::GetHostEntry($Computer) 
                $OS = Get-WmiObject win32_operatingsystem -ComputerName $Computer -ErrorAction Stop -Credential $Credential 
                $BootTime = $OS.ConvertToDateTime($OS.LastBootUpTime) 
                $Uptime = $OS.ConvertToDateTime($OS.LocalDateTime) - $boottime 
                $propHash = [ordered]@{ 
                    ComputerName = $Computer
                    BootTime     = $BootTime
                    Uptime       = $Uptime
                    } 
                $objComputerUptime = New-Object PSOBject -Property $propHash 
                $objComputerUptime 
                }  
            catch [Exception] { 
                #Write-Output "$computer $($_.Exception.Message)"
                           $propHash = [ordered]@{ 
                    ComputerName = $Computer
                    BootTime     = "Unavailable"
                    Uptime       = "Unavailable"
                    } 
                $objComputerUptime = New-Object PSOBject -Property $propHash 
                $objComputerUptime
                #return 
                } 
        } 
    } 
    end{} 
}

#Variables
$OutputFile="C:\Scripts\Tools\GetAllServersUptime.csv"
$UptimeHTMLReport="C:\Scripts\Tools\UptimeCheckServer.html"
$MailTo=""
$MailFrom=""
$SmtpServer=""


#MAIN

#Deleting all result files
If(Test-Path $OutputFile){
    Remove-item $OutputFile -confirm:$false -force
}
If(Test-Path $UptimeHTMLReport){
    Remove-item $UptimeHTMLReport -confirm:$false -force
}

Add-Content -path $OutputFile -value "ServerName,LastBootTime,Uptime"

#Fetching list of all Servers in AD
$Serverlist=Get-ADComputer -Properties * -filter {OperatingSystem -like "*Server*"}

    $htmltableheader = '
<style type="text/css">
.myTable { background-color:#FFFFE0;border-collapse:collapse;font-family:Georgia, Garamond, Serif;color:black; }
.myTable th { font:bold 18px/1.1em Arial, Helvetica, Sans-Serif;text-shadow: 1px 1px 4px black;letter-spacing:0.3em;background-color:#BDB76B;color:white; }
.myTable td, .myTable th { padding:5px;border:1px solid #BDB76B; }
.myTable td { line-height:2.5em; }
</style>
<h3 align="Center">Uptime Check Status</h3>
                        <p>
                        <table class="myTable" align="Center">
                        <tr>
                        <th align="Center" width="60">Status</th>
                        <th align="Center">Server</th>
                        <th align="Center">LastBoot</th>
                        <th align="Center">Uptime</th>
                        </tr>'
Add-content $UptimeHTMLReport -value $htmltableheader

$imgsrc='<img src ="http://apps.campusops.oregonstate.edu/emergency/images/EmerPrep/alertlight.png"  width="40" height="40">'
$ImageKO='<img src ="https://openclipart.org/download/285479/Thumbs-down-Circle.svg" width="40" height="40">'
$ImageOK='<img src ="https://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Green_check.svg/480px-Green_check.svg.png" width="40" height="40">'
$ImageAVG='<img src ="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTRN2qS4vBKcDpgdIcxMOIVWDcoxS0w8a6t8jV62zdXKyMIhFRXPw" width="40" height="40">'
#Processing
$ServerList | Foreach-object{

    $Servername=$_.Name
    Write-host "$ServerName - " -nonewline
    $GetUptime=Get-Uptime $ServerName
    If($GetUptime.Uptime -ne "Unavailable"){
        $LastBoot=$GetUptime.BootTime
        $Uptime=$GetUptime.Uptime
           [int]$UptimeDays=$GetUptime.Uptime.Days
    }
    If($GetUptime.Uptime -eq "Unavailable"){
        $LastBoot="Unavailable"
        [string]$Uptime="Unavailable"
           [string]$UptimeDays="Unavailable"
    }
    Add-content -path $OutputFile -value "$ServerName,$LastBoot,$Uptime"
       If(($UptimeDays -gt 90) -and ($UptimeDays -lt 150) -and ($Uptime -ne "Unavailable")){
             $UptimeDays=$Uptime.Days
             Add-Content -path $UptimeHTMLReport -value "<tr>
                            <td align='Center'>$ImageAVG</td>
                                               <td align='Center' bgcolor=yellow>$ServerName</td>
                                               <td align='Center' bgcolor=yellow>$LastBoot</td>
                                               <td align='Center' bgcolor=yellow>$UptimeDays</td>
                                               </tr>"
       }
       If(($UptimeDays -ge 150) -and ($UptimeDays -ne "Unavailable")){
        Write-host "$UptimeDays" -foregroundcolor:Red
             Add-Content -path $UptimeHTMLReport -value "<tr>
                            <td align='center' >$imgsrc</td>
                                               <td align='Center' bgcolor=red>$ServerName</td>
                                               <td align='Center' bgcolor=red>$LastBoot</td>
                                               <td align='Center' bgcolor=red>$UptimeDays</td>
                                               </tr>"
       }
       If(($UptimeDays -lt 90) -and ($UptimeDays -ne "Unavailable")){
             Write-host "$UptimeDays"
             Add-Content -path $UptimeHTMLReport -value "<tr>
                            <td align='Center'>$ImageOK</td>
                                               <td align='Center' bgcolor=green>$ServerName</td>
                                               <td align='Center' bgcolor=green>$LastBoot</td>
                                               <td align='Center' bgcolor=green>$UptimeDays</td>
                                               </tr>"
       }
       If($UptimeDays -eq "Unavailable"){
             Write-host "Unavailable" -foregroundcolor:yellow -backgroundcolor:blue
             Add-Content -path $UptimeHTMLReport -value "<tr>
                            <td align='Center'>$ImageKO</td>
                                               <td align='Center'>$ServerName</td>
                                               <td align='Center'>$LastBoot</td>
                                               <td align='Center'>N/A</td>
                                               </tr>"
       }
}

Add-Content -path $UptimeHTMLReport -value "</table>"

Write-host "OK" -foregroundcolor:Green
$htmlreport=Get-content $UptimeHTMLReport | out-string
Send-MailMessage -SmtpServer $SmtpServer -To $MailTo -From $MailFrom -Body $htmlreport -BodyAsHtml -Encoding ([System.Text.Encoding]::UTF8) -subject "[UPTIME] Audit Servers" -Attachments $UptimeHTMLReport

Don’t forget to modify those lines :

$OutputFile=”C:\Scripts\Tools\GetAllServersUptime.csv” $UptimeHTMLReport=”C:\Scripts\Tools\UptimeCheckServer.html” $MailTo=””

$MailFrom=””

$SmtpServer=””

And enjoy !