|Normally, except in rare cases, the only thing that sometimes can make a clicking noise occaisionally is a hard drive that's still spinning.|
Depending on which activity led it is, that can be on and flash when the Windows is Shut Down properly - e.g. sometimes leds on network adapters do that - but if it's the hard drive activity led that's doing that, your mboard is definately in Standby or Hibernate mode, whether it should be or not.
It sometimes doesn't matter what your settings in Windows are regarding Standby in Windows are if something else is not right - your computer may go into Standby or Hibernate mode anyway when you attempt to Shut Down Windows.
The most common reason for that is Windows doesn't have the proper info about how the ACPI support of your mboard works, which can determine whether or not Standby, Hibernate, Shut Down, etc. works properly.
Usually that's caused by you or someone who did it for you loading or re-loading Windows from scratch and NOT loading the main chipset drivers, which include the info Windows needs to know about the ACPI support the mboard has.
In the case of Windows XP, it was first released in 2002? and what it can recognize with what is built into it has not changed much since, even with the SPx updates. It is likely that when your mboard is newer than that, it can't find all the info it needs to know about your mboard on it's own.
Whenever you load Windows from a regular Windows CD (or DVD) from scratch, after Setup is finished you must load the drivers for the mboard, particularly the main chipset drivers, in order for Windows to have the proper drivers for and information about your mboard hardware, including it's AGP or PCI-E, ACPI, USB 2.0 if it has it, and hard drive controller support. If you have a generic system and have the CD that came with the mboard, all the necessary drivers are on it. If you load drivers from the web, brand name system builders and mboard makers often DO NOT have the main chipset drivers listed in the downloads for your model - in that case you must go to the maker of the main chipset's web site, get the drivers, and load them.
If that's not what caused your problem, other things can cause the computer to not Shut Down properly and go into Standby or Hibernate mode rather than than the mboard shutting off completely.
Probably the most common cause of that is some software you have loaded is causing the problem.
Remove any bootable CDs or DVDs you have in drives.
If your computer is actually going into Standby or Hibernate mode instead of shutting off comletely, doing this should make it shut off completely....
Hold the power button in until the mboard shuts off completely - on most ATX computers that takes 4 seconds or more - the activity led and any other leds will go off and stay off, other than possibly one for a network adapter or a mouse which may stay on, and no drive or fan will be spinning. You should hear no clicks - normally, only a hard drive that is still spinning can make that noise.
(Some higher end PSs continue to spin a fan at a slow speed for a short time after you have shut down Windows.
Rarely: some power supplies have been known to make tiny noises after you have shut down Windows, when they still have live AC being supplied to them.)
Repeatedly press F8 while booting, don't hold down the key, starting very early in the boot sequence.
When the boot choices menu appears, select Enable VGA mode.
That loads everything normally, except it forces the video to use default VGA drivers instead of the specific drivers you have loaded for the video.
Once the desktop has loaded, Shut Down Windows.
If doing that shuts the mboard off properly, your problem has something to do with the specific video drivers you normally load when you boot normally.
E.g. a friend of mine's laptop had that problem - I loaded an older video drivers version for his integrated video and the problem disappeared.
Or - the problem may be cured by loading a newer version of them, or drivers from an alternate source.
In his case, I got the older drivers from the Sony site, rather than from the Intel site.
If the mboard still does not shut off properly when you boot into Enable VGA, try booting while repeatedly pressing F8 again, and choose Safe mode from the boot choices menu.
Once the desktop has loaded, Shut Down Windows.
If the mboard then shuts off properly, something that Safe mode does not load that booting normally loads is causing your problem, but it probably has nothing to do with the specific video drivers you load when you boot normally.
It can sometimes be caused by a defective power supply, but that's extremely unlikely in your case since you have an Antec PS.
The only way to tell for sure is to try another PS that has enough capacity with your mboard - borrow one from a working system temporarily if you can if you want to try that.