SharePoint displays users as Domain\Username instead of Display Name

Login to sharepoint by farm account and launch powershell

1. If the problem only appears with a single user, you can update a single account like so:

Set-SPUser -Identity ‘domain\Username’ –Web http:// –SyncFromAD

2. If all (or a lot) of the uesrs you can do it by the following:

Get-SPUser –Web http:// | Set-SPUser –SyncFromADS