Get all Text after a character 
$string = "1. Computer name:DC-G11-FTW.contoso.com"
$string.Substring($string.IndexOf(":")+1,$string.length-$string.IndexOf(":")-1)
Details
Uses a substring and IndexOf to break apart the string

Example
PS C:\> $string = "1. Computer name:DC-G11-FTW.contoso.com"
>> $string.Substring($string.IndexOf(":")+1,$string.length-$string.IndexOf(":")-1)

DC-G11-FTW.contoso.com
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