Problems Downloading Video Files

>-----Original Message-----
>Often after I have downloaded video files, they will not
>play on Win Media Player.
>
>Error messages include Win Media Player Encountered An
>Unkown Problem or an error message about a certificate
>problem.
>
>How do I know if it is a corrupt file or a problem with
>my computer?
>
>Any solutions ??
>
>Thanks All !
>.
>