How Can I fix my Thomson DTR6300?

I've been trying to watch a programme, but the picture on the box constantly glithers, for the last week or so. I've switched the box on & off, unplugged the box, cables & even re-scanned the box on several occasions, but still no joy. It may be the cables, but tried 2 get the scart leads in proper. Picure on tv is ok without the box being switched on I don't think it's the Ariel Cable which is going to the box, but 2nt be sure. PLEASE CAN ANYBODY HELP ME! Kerry