I also hear slow clicking noise and fan moves a little when it clicks sometimes starts sometimes it won't then turn psu off and try again until it does
If it still acts up, compare wiring of the large motherboard Molex connector to the original. Dell used a variant that does not interchange. The enable wire is in a different location from standard ATX location.
If the processor is an AMD, remove cbattery and clear BIOS, and then try again.
SOURCE: Pulsating hard drive on startup and off
To eliminate a software problem, I installed another hard drive with the same operating system, and the problem still existed.
I also flashed the BIOS with no results.
The most logical conclusion is that the problem lays with power supply.
A new power supply was ordered today.
SOURCE: PC won't start. Unit is getting power but fan
I suspect you are spot on. Time to fork out for a new one methinks
SOURCE: Dell Optiplex GX280 Power switch flashes white
Outlet - unplug the power cable and put it on an outlet on its own
Power Cord - make sure you remove the power cable from the back and plug it back in to make sure you have a good connection.
things that cause this blinking light:
Power Supply -open system and follow cables to make sure its connected well to each part.
I/O Panel - this is where the power button is at . just open the system and follow it behind the power button.the flat cable going to the mother board , disconnect it. plug the power cable to the wall and if the system starts up then the power supply is good and the the cable that you just disconnected is bad.
If it still doesn't power up remove
memory
hard drive
dvd/cd drive
and start the system.
no luck then it is the systemboard.
SOURCE: I have a Dell 8400
More than likely what you have been told is correct. Test it with a multimeter. Turn the PC off but do not unplug it. Remove the side panel. Set the multimeter to DC volts at the next setting higher than 12 volts DC. Locate a power connector like the one going to the CD drive or hard drive connector that is not used. Turn on the PC and connect the black probe to the black wire on the power connector. Connect the red probe to the yellow wire connector. The meter should read +12 volts. Now touch the red probe to the red wire and it should read +5 volts. If not reading or reading different that this the power supply is bad and needs replacing. If the readings are correct then check the P8 or P9 connectors at the motherboard. They may be labeled P4 and P5. Connect the black probe to P8 black wire and red probe to P8 red wire. It should read +5 volts. Now insert the red probe at P8 to the yellow wire and you should get +12 volts. Now check the blue wire and it should read −12 volts. Move the black probe to the black wire on P9 connector. Check the white wire with the red probe and it should read −5 volts. Check the red wires on the P9 connector and you should get +5 volts on each red wire. If the reading is close such as 5.02 volts then it is ok. But if the readings are off by a couple of volts as in 10 volts instead of 12 volts the power supply is bad. Be very careful and if you are not comfortable doing this have it tested by a pro.
SOURCE: Can not get computer to
Bad Power Supply, sscorbett.
Usually you have enough power to light LED lights, (Like the harddrive activity LED light for add-in cards, that you see on the motherboard), and spin fans, but Not enough power to turn the Processor on.
Dell Support >Dimension 8400 > Service Manual
http://support.dell.com/support/edocs/systems/dim8400/SM/index.htm
Technical Overview > System Board Components
http://support.dell.com/support/edocs/systems/dim8400/SM/techov.htm#wp1052739
harddrive activity light for add-in cards (SCSI LED)
The Dimension 8400 comes with an ATX style of Power Supply, that has a maximum rated Wattage of 250 Watts.
1) ALL of the LED lights combined use less than 1 Watt of power.
2) EACH fan uses 2 to 3 Watts
3) A typical Processor can use 51 to 125 Watts.
Your Power Supply just has enough power to light that LED light.
Weak voltage power rail.
Replace the Power Supply.
[ There are three power rails inside that SMPS.
Switched-Mode Power Supply.
1) The 3.3 Volt power rail
2) The 5 Volt power rail
3) The 12 Volt power rail ]
The ATX form factor for a Power Supply refers to the size, and shape of the case, for one.
Approximately 6 inches Wide, 5.5 inches Long, and 3-1/2 inches Tall.
The ATX power supply case in the Dimension 8400 however, is shorter in length.
It is 4 inches Long. (Depth)
Not an advertisement for the website, nor manufacturer.
Reference for the case size, and power cables needed,
http://www.cputopia.com/hp-400w-dell-dimension-8400.html
Scroll down to see the connectors of the various power cables needed.
You may have a Power Supply with these dimensions, and needed power cables, in an unused computer.
Perhaps someone has upgraded to a better computer, and has an unused computer that you can temporarily borrow the Power Supply for a test unit.
Make sure it has at least 250 Watts (Maximum rated wattage), plus,
1) 20-pin ATX main power cable. (Or a 20 + 4-pin ATX main power cable)
http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20
[ 20 + 4-pin ATX main power cable,
http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20plus4 ]
2) 4-pin ATX +12 Volt power cable
http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
Plus the various power cables needed for the Harddrive, optical drive/s, and computer case fan/s, if it/they do not connect to the motherboard.
I also have a Dell 8400 heat problem . I know the problem ! I own a $1000.00 plus Raytek laser temp gun . I had some problems and started to read about all of the Dell 8400/4400 over heating problems . I out my new heat gun and started to test the temps. on the inside of my Dell 8400 ! Socket 775,Mobo Dell 0J3492,800 Bus,Bios A09.
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i should add already replaced psu
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