Hi Colin,
Can you give us more details about the hardware in your machine and also what changes you made , i.e. what program(s) you installed at the time the trouble started. It may be nothing more than a driver and/or program update being required, but then again it could be something else altogether. The more information that we have, the easier it is for us to help you. This is why it is essential that people fill in their System Specs section of their CP as comprehensibly as possible - see mine for details of the type of information required.