15" MacBookPro Dvi - HDMi with Toshiba TV

Trying to use a newish Toshiba 32XV505D as a mirrored monitor for films played on my Intel Core Duo MacBook Pro running 10.6.3. It worked for a short time although I couldn't get any sound with the recommended 3.5mm sound lead. I disconnected while I sorted the lack of sound and when I connected it again - nothing. The Mac detects the TV and shows it in the display menu(as does SwitchResX)but the TV only displays a blue(is that no signal?)screen. I've used a long Dvi to hdmi lead that works on our larger Samsung TV but can't get it or a new shorter lead to work. Made sure the HDMi ports are selected on TV and been through all the changeable resolutions on the Mac but still no joy. Made sure mirroring is selected on the Mac. Tried disabling Regza and lip sync. on the TV (in case CEC is the problem) but no joy. ..... Help please....