My dell home computer is making a clicking noise and will not start

Would help if you can get indicators from the system like the color of the light on its power button and if it is blinking, the system may also have 4 small lights in its front or back panel which will also give indicators of the system. Things you can try to do to start isolating the fault is to remove the power cables and the data cables from all your drivers (hard disk, dvd/cd), and remove and reconnect the front I/O panel where the power button is located, remove and reconnect the power connections to the motherboard, remove and reconnect only a 1 working memory module, then try to turn it on again. Try to determine if any indicators change and try to pinpoint the source of the noise. it is possible that this can be from the hard drive, the power suppy or the fans on the system board. if it is from the fans or the power supply, those are the components to replace. if the noise stopped, try to reconnect the hard drive first and test it, then proceed with the CD/DVD drive. If you've isolated the fault, you can then proceed to get the needed replacement.