FIM Powershell Password Reset Workflow

Question

Hello All,
I'm trying to use the FIM portal in order to allow helpdesk to reset an users password upon the end user calling helpdesk. But am running into an issue with the powershell workflow.
Currently I have added a boolean attribute called "PasswdReset" and binded it to the user type.
Created an criteria based set called "PasswordResetUsers" which will transition users into when passwdrest is set to true.
Created an workflow called "PasswordResetWF" which is made up of several steps
1. The powershell activity which executes the following script
Import-Module Activedirectory
$newpwd = ConvertTo-SecureString "P@ssw0rd" -AsPlainText –Force
Set-ADAccountPassword SampleUser -Credential domain\administrator -NewPassword $newpwd -Reset -PassThru | Set-ADuser -ChangePasswordAtLogon $True
Here lies the problems
First how do I pass the samaccountname of the user to the powershell script to replace the sampleuser parameter.
Second How do I  force this script to run as the domain\administrator without prompting for password
The rest of the workflow is as follows.
2. Trigger custom email notification to an monitored email account for logging purpose
3. Trigger custom email notification to Helpdesk monitored email account to generate support ticket. 
4. OOB function to set "PasswdReset" attribute to false and transition the user out of the "PasswordResetUsers" set.
As always any suggestions would be greatly appreciated. 

Answer 1

Peter,
Thanks for your reply.
Had another look; events are indeed present;
Log Name:      Application
Source:        PowerShellActivity
Date:          01/04/2015 17:45:31
Event ID:      0
Task Category: None
Level:         Information
Keywords:      Classic
User:          N/A
Computer:      SERVER.DOMAIN
Description:
01/04/2015 16:45:31 -- Executing: Import-Module Activedirectory
$newpwd = ConvertTo-SecureString "P@$$w0rd" -AsPlainText –Force
Set-ADAccountPassword $fimwf.WorkflowDictionary.samAccountName -NewPassword $newpwd -Reset -PassThru
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="PowerShellActivity" />
    <EventID Qualifiers="0">0</EventID>
    <Level>4</Level>
    <Task>0</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2015-04-01T16:45:31.000000000Z" />
    <EventRecordID>50286</EventRecordID>
    <Channel>Application</Channel>
    <Computer>SERVER.DOMAIN</Computer>
    <Security />
  </System>
  <EventData>
    <Data>01/04/2015 16:45:31 -- Executing: Import-Module Activedirectory
$newpwd = ConvertTo-SecureString "P@$$w0rd" -AsPlainText –Force
Set-ADAccountPassword $fimwf.WorkflowDictionary.samAccountName -NewPassword $newpwd -Reset -PassThru</Data>
  </EventData>
</Event>
In my case, it was password policy.
Thank You!