one of the tasks I want to automate is changing my computer name from an user input. 

$rename = read-host "please enter the computer name:"
write-host "will change to $rename" -foregroundcolor black -backgroundcolor white
$computername = Get-WmiObject Win32_ComputerSystem
$computername.Rename($rename) 
Restart-Computer

This script runs fine but my computer name doesn't change. I'd like to know what I did wrong/

Hi Ex Maxina,

make sure the account is permitted to perform this change and try running it elevated.

Also, the method definition of Rename wants three parameters, so maybe this will be more successful:

$computername.Rename($rename, $null, $null)

Cheers,
Fred

hello,

Are you on Powershell version < 3?

if not you could use CmdLet rename-computer

get-help Rename-Computer

If you have proper permission you can pass user ID and password as arguments of Rename Method

(Get-WmiObject -Class Win32_ComputerSystem).Rename

OverloadDefinitions                                                                                                
-------------------                                                                                                
System.Management.ManagementBaseObject Rename(System.String Name, System.String Password, System.String UserName)

Sample Code

$credential = Get-Credential
Get-WmiObject Win32_ComputerSystem -ComputerName OLDNAME -Authentication 6 |
ForEach-Object {$_.Rename("NEWNAME",$credential.GetNetworkCredential().Password,$credential.Username)}

Rename-Computer is much easier.

https://technet.microsoft.com/en-us/library/Hh849792(v=wps.620).aspx