Archos 80 frozen Help !!

[playford]

I was browsing the Web using Dolphin browser and selected a link to sky sports.
I now have a Security Warning saying there is a problem with the security certificate.
There are 3 options, Continue, View Certificate and Cancel but I am unable to select any of them as the Archos has frozen.
I held the on off button down for 20 seconds but nothing happens.
How do I reset the thing ??
Thanks

Kevin

[RhysD123]

Put it on charge,It happend to me aswell.