Hp m8400f power up problem

http://www.engadget.com/products/hp/pavilion/media-center/m8400f/specs/

Hello, it sounds like the the graphics processing unit has over heated and has a bad connection on the motherboard. There is a repair for this and it requires a desoldering station, thermal paste, and fan modding if your up to the challenge it can be done. Hope this helps.

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Power Supply problem Bob.

Weak voltage power rail.

Allow me to explain what is going on;

1) Monitor is working OK. Shows No Signal.
Means No Video signal is getting to the monitor. This is because the computer isn't working.
Monitor goes to Sleep Mode, or Power Saver Mode, to conserve power.

2) Orange LED comes on, and fans spin.
Means NOTHING.

Light Emitting Diode, so it is a LIGHT.

A) If ALL the LED's were on at once, they would use LESS than 1 Watt of power.

B) EACH fan uses 2 to 3 Watts of power.

C) A typical CPU (Processor) uses 51 to 125 Watts of power.

Hmmm, HP Pavilion M8400f Desktop PC?

http://h10025.www1.hp.com/ewfrf/wc/product?product=3686665&lc=en&cc=us&dlc=en&lang=en&cc=us

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01374051&tmp_task=prodinfoCategory&cc=us&dlc=en&lang=en&lc=en&product=3686665

(Showed you the path)

Hardware / Base Processor;
AMD Phenom-9500 (A) 2.2 GHz (95W)

Uses Up To 95 Watts of power.

This is why the simpy LED's light, and fans spin; BUT there is NOT enough power to turn the Processor (CPU) on.

Method to repair is up to you Bob, but I would recommend testing the 3 main voltages coming out of the Power Supply, with a multimeter; OR using a KNOWN to be good, Compatible power supply for a temporary test unit.

Or you can buy a replacement Power Supply.

I would just like you to test the Power Supply, or use a temporary replacement, so you do not rush out, and buy a Power Supply; and find this wasn't the problem.

A economical multimeter, (But is plenty good enough for this test), can be purchased for as little as $5 to $12.
An auto parts store is bit one example. (Although usually a little more pricey)
I have seen them on checkout aisle racks, at major discount stores.

The dangerous (100 to 240 Volts AC. Depends on what country you are in), voltages are KEPT within the metal case of the Power Supply.

The voltages coming out are 3.3 Volts, 5 Volts, and 12 Volts.
All are DC Voltage.
In comparison two D cell flashlight batteries produce 3 Volts DC.

Replacement Power Supply?
Try the easy method.
Type - Pavilion m8400f power supply in your search bar, and press the Enter key,

From one search hit,

http://www.sparepartswarehouse.com/HP,Media-Center,m8400f,KJ377AA,Computer,Power-Supply.aspx

To the right of View Details states 5188-2625
That is the HP part number
HP 5188-2625

Search HP 5188-2625,

http://www.amazon.com/s?ie=UTF8&keywords=hp%205188-2625&page=1&rh=i%3Aaps%2Ck%3Ahp%205188-2625

This particular search hit has various examples shown.
ALL examples are ATX.

ATX is a Form Factor,

http://en.wikipedia.org/wiki/Computer_form_factor

Originally designated for Motherboards. (Mainboard)
Went to Power Supply's, and computer cases, also.

An ATX form factor for a Power Supply, designates it's size, and shape; plus the types of power cables coming from it.
(Also the inherent technology)

Size and Shape:
Approximately 6 Inches Wide, 5.5 Inches Long, and 3-1/2 Inches in Height.
(152.39mm Wide x 139.7mm Long x 88.89mm in Height)

If you buy an ATX power supply nowadays, it will have the correct power cables you'll need, and probably ones you do not need, plus more than you need.
Works out pretty good, huh? Just wrap the power cables you do not need, with PLASTIC tie strips, and up out of the way.

(DON'T use bread ties. They have a metal strip in the middle)

The original Power Supply is reputed to put out a Maximum rated Wattage of 300 Watts.

KNOW THIS,
A computer ONLY uses the power it needs, and NO MORE.
If you put a 10,000 Watt Power Supply in, and the computer only needs 100 Watts for what it is doing, it ONLY uses 100 Watts.

You should use a Power Supply, that is rated at least 10 percent more than what is needed.

One example of a replacement Power Supply,

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3276575&CatId=1078

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00583783&tmp_task=useCategory&cc=us&dlc=en&lang=en&lc=en&product=3686665

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01358091&tmp_task=useCategory&cc=us&dlc=en&lang=en&lc=en&product=3686665

I can step by step guide you in testing the voltages, with a multimeter; and also in replacing your Power Supply.
Post back in a Comment.

Regards,
joecoolvette

Maybe a boot issue.
If you got some CD with your computer when you buy it, try to start your computer with one of these CD into the CD drive.

Can you try going into safe mode?

Press F8 while boot process and use safe mode to boot into windows.

In my case it turned out to be a weak power supply. It would work sometimes and not others. If stone cold, it would not boot. If I unplugged 1 thing, like the hard drive or the CD Roms, it would boot. Tested the old power suppy and it seemed to pass. But once I connected a new power supply, the computer has worked fine ever since.

Please have a look at this article and consider updating the BIOS: click here

I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
If I've managed to answer your question or solve a problem, please take just a moment to rate this post....thanks!

I think your motherboard has gone bad, even though you hear a fan working, its just on a hot wire on the motherboard.

pull the power cord out and the battery (or just let it run out). Then, try turning it back on again. If it does the same thing again then yes it may be old blue death and your harddrive may be worse than dead. I don't believe that the power button doesn't work. Hold it in for 10-15 seconds or so, any computer is DOS programmed to respond to the power commands above all, even above the dreaded blue screens. Let me know if I'm an ******* and I don't know what I'm talking about or if you need more help.

Dismantled notebook thinking compressed air removed component or connection. Nothing. Reassembled most of notebook. Left battery and power disconnected for 6.5 hours, I later plugged only AC power into unit. Fans started spinning. Completed assemble of notebook and installed the battery. Blue lights returned. Problem seems to be the battery. Shorts out something and needs about 6 hours drain out. Works great now without battery, using AC power only. Ordered new battery.....