Top up TV software appears to be causing the problem...
http://www.topuptv.com/help+centre/setup+and+troubleshooting/Fail+boot+up
This gives you two procedures to go through. The first seems to be working for most people - although it can take many attempts, and you need to be very quick.
The second reformats the whole box, so you lose all your recordings - I would try the first one quite a few times first.
Claire
May 2009