Without knowingly changing anything my SW2013 has developed a peculiar characteristic. When I select 'Preview Window' for even the most simplest of parts the black empty preview window appears immediately and stays there for perhaps 45 seconds without any activity and then the part appears normally at normal speed. It does this with a simple part or complex assembly. All other SW operations are normal.
If I select 'Final Render' the whole process is held up until this Preview Window delay has elapsed.
Does anyone know why this might occur? Can I invoke any default settings to try and clear this problem or should I just try a fresh install of SW2013?