|ATX mboards are always powered in some places even when the computer is not running, as long as the PS is connected to the mboard, the PS is switched on if it has a switch, and the PS is receiving live AC power. |
Also, the PS can be damaged from you merely plugging something else such as the power connector to a drive in that situation.
To avoid damaging something...
Unplug the computer / PS, or otherwise switch off the AC power to the computer BEFORE doing anything inside the case.
Plug in the computer / PS or otherwise switch on the AC power to the computer / PS AFTER you have connected everything else.
You must have at least one ram module, and the video card installed, and have a keyboard and mouse plugged in.
If you don't plug in the power for the hard drive, if it does boot, you may get an error while booting regarding an operating system not being found or similar.
If your system has a floppy drive and it is hooked up, if you don't plug in the power for the floppy drive, if it does boot, you may get an error about the floppy drive not being found or similar.
Be careful that you get the power connector plug for the floppy drive on the pins on the drive properly - it's possible with the design of some floppy drive's power connectors (male - usually 4 pins) to not get the plug (female) from the power supply on the right pins.
Getting the power connector on the wrong pins can fry the floppy drive's board.
If you have not upgraded the video card, a PS with a capacity of 300watts or more will do - it might even be fine with a 250 watt one.
You need to plug into both the main 20 "Pin" power socket, and a smaller 4 "pin" one near the corner of the CPU socket, on the mboard.
If the PS you try has 24 pins in it's main power connector, 4 of them on one end are usually removable - the 4 pin connector slides off or un-clips.
I took a look at the manual for your mboard.
Desktop Board D875PBZ
April 9 2003
No onboard video
20 pin main connector
A second 4 "pin" power socket near the corner of the cpu socket- B on Page 63
AGP - Page 29 - 1? / 4 / 8; 2X not supported
Install memory in the DIMM sockets proir to installing the AGP video card to avoid interference with the memory retention mechanism
My note - make sure the memory is all the way down in it's slot(s) and the clips on both ends of the ram slots(s) are against the ends of the module(s).
Cable must be shielded
connector page 71
Bios Setup configuration jumper
Page 14 - W - and Page 72 - location
Page 73 - settings
You use 2-3 when you change which cpu is installed, then move it back to 1-2
Page 69 front panel connector.
Make sure the wiring connectors are all the way down on that
While you're in there, if the cpu fan/heatsink has mung (dust, lint, etc.) on it, clean it off, but DO NOT use a vaccuum cleaner to do that (they produce a tremendous amount of static electricity when running, and anything connected to them can discharge that to your components) - use canned air, or an air nozzle if you have access to an air compressor, or an artist's brush that can be used in small spaces, etc. It may be difficult to clean the top of the heatsink under the cpu fan - the most likely place to have mung on it - and the bottom side of the cpu fan blades unless you remove the fan. If you have a case fan, clean that too if it needs it.
Also check for mung on the video card fan and heatsink if it has that, and the power supply's openings / fan.
With the cover still off, restore the AC power, start the computer and make sure the cpu fan spins - if it doesn't spin, if you're sure the power supply is working okay, don't use the computer until you have replaced it.
If it spins too slowly, and/or if it makes rattling or screeching noises, most likely to be noticed when the computer has cooled to room temp, has not been used for a while, and then is started up, the cpu fan's bearings are failing - the cpu is likely to overheat as a result of that if it can no longer spin it's full speed - replace it as soon as you can.
If you have upgraded the AGP video card, or if you think you might upgrade it in the future,....
Your power supply must have at least the minimum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video - video built into the mboard - IS NOT A CARD ! )
If that info is not in the ad for the video card, you can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. Some power supplies have two or more +12v ratings - in that case, add those ratings to determine the total +12v current capacity.
If you're a gamer...
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It's recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should get.