The problem came about when I purchased a new Thermaltake case that has 2 Sata Ports on the top to enable quick change of sata hard drives, and which required me using 2 additional 4 pin molex cables.
I also have 2 dvd drives (1 is a Sata cable and 1 uses an Ide Cable) and 2 Sata Hard Drives and 1 Floppy disk drive (an Imation 120Mb drive).
The case also has an extra 2 Case Fans which also have to plug into the 4 pin Molex cables.
If I unplug the floppy drive and one of the DVD Drives everything works fine. The problem that arose when I had everything connected was a noisy hard drive spinning at difeerent speeds.
Thanks for your prompt reply to my original question.
John from Australia
If there's a problem powering up your gear then this might suggest that your PSU isn't of good quality or you have exceeded its rated wattage. Also bear in mind that PSU's performance, degrades over time and what might work for a few years doesn't mean it will work for ever...