Thank you for the advice so far. The problem is that the PC "hangs" on start up, the icons appear and then the clock dissappears, if I put the mouse over the blank taskbar the egg timer appears. The processor has stopped clicking by this time and nothing else happens.
Richard...I have always read your informed comments with interest, the CD is a direct replacement for another and is the only device connected to the ribbon, it is also set as master. I tried a reboot with the cd disconnected but nothing else changed. I know the cd works because it allowed me to load the software before the reset button was pressed in error. I have this cd on my own PC with Nero and it works perfectly.
I am prepared to try anything except reformat as all the files and programs are there in safe mode.