Please can anyone help me here.

I'm used to Tixati opening up when I decide to choose to download a torrent.
This does not happen since getting a new computer.

I've now got a windows 8.

Please can anyone assist me here please?

Thank you

That's set in your web browser. Look for options about how files opened by external applications are handled. For instance, in Firefox it would be "Tools -> Options -> Applications".