Yesterday my computer would not boot up. I would hit the power button and all the fans would come on, but none of the IDE components seemed to be recieving power.
After some poking around under the chassis, i discovered that when i disconnected the IDE cable from the DVD-ROM, the rest of the components (CD-ROM, 2 Hard Disks) would power up just fine and the computer functioned normally. Today when i went to power up the computer, ALL of the IDE components seem to suffer from the same issue.

*When the IDE components are connected ONLY TO THE PSU the component recieves power. However when i connect the component to the Motherboard via the IDE cable, the component does NOT power up. For instance, when i connect the Hard Disk only to the PSU and I turn the computer on i can feel the Disk spinning; however when i connect it to the Motherboard, the disk does not spin. When I run the same experiment with the CD or DVD-ROM, i can open the tray when the component is connected only to the PSU, however when connected to the Motherboard, I am unable to open the tray.

Does this mean there is a short somewhere on the Motherboard?

Hello vril and welcome to the http://www.pcguide.com/ubb/pcgubb.gif forum!

It could very well be the motherboard is going out; however, my gut instinct is that it could be the PSU itself. Power supplies have been notorious for going out little by little in subtle ways or sometimes they just flat go out. If your fans are still running on the motherboard, it means the PSU is still putting out enough power on those lines to power the fans; however, the fans take the littlest amount of power to run. It could be that once you connect the hard disks (or cd-rom drive) the BIOS's calling them into active mode then causes the drive to consume more power than the PSU can supply, thus a dip in power.

Have you recently installed any new hardware on the motherboard (e.g. Video cards, PCI Cards, Memory, new drives etc.)? If so then your PSU might be at its limit of power output.

Test your PSU by following this quote by Sylvander: (Make sure you test them under a load, i.e. connected to a drive)

TESTING ATX POWER VOLTAGES

See this http://www.ochardware.com/articles/psuvolt/psuvolt2.html
And this http://www.pcguide.com/vb/showthread.php?s=&postid=152496#post152496

Black = ground
Red = +5 volts
White = -5 volts
Yellow = +12 volts
Blue = -12 volts
Orange = +3.3 volts (?)
Green = power on

Turn the power on. The fans should at least come on so that you know you have power.

Turn on the voltmeter and set it to measure DC voltage. Start with an IDE power connector that is not used. Place the black lead of the voltmeter in the hole of the connector that has a black wire (ground). Connect the red lead of the voltmeter first to the yellow hole and then to the red hole. The voltmeter should read +12v and +5v respectively.

The other voltages may usually be measured at the motherboard power connector by simply sliding the red multimeter test probe down the hole where each colour wire goes (with the black probe connected to any black wire as before). Really you only need to check the orange wire for 3.3 volts at this connector. If +12, +5, and +3.3 volts are all okay, then your power supply is probably fine.

Unfortunately, a low voltage measured in this way may mean a bad PSU or that some other component (motherboard, etc.) has a short and is pulling the voltage down. Therefore, the main value of measuring voltages is to eliminate the PSU as a source of the problem (if it has normal voltages).