HP Pavillion Elite Startup Problems:
A friend of mine told me his Computer would not Startup to Windows. It had a Black screen.
The black screen reminded me of the last one I repaired a HP pavillion A1646x. It had all the same symptoms.
I checked inside the Computer and verified that all PCI cards, Memory and Power Supply connections were solid. Then I tried to Boot the Computer, I didn't here any beep codes (sound). and the motherboard LED was on.

I rebooted to check the Bios to verify that the hard-drive was installed and active. No problems there.
I basically did some tests like I did to the HP Pavillion a1646x above. I visited HP website and reviewed their troubleshooting guides.
I reviewed the section on power supply lite being on or off. This one was on.  I review the guide about the Power Supply light being off and instructions.

It appeared to me the power supply was good based upon HP guides. So I proceeded to TS the HDD and Bios.
After TS the HDD and Bios I decided its got to be a loose connection. I verified everything was connected properly and still no boot..

I then thought maybe it was the Motherboard although its light was on and the power supply light was on. my last choices. I decided the only way I knew to check both MB and PS was to change out the power supply first, I removed a power supply from one of my spare Computers (this one) and Installed it and the Computer Booted up normal.
I let it run and let all the updates install .
Power supply light
This page was last updated: June 17, 2011
At least the Power Supply light works
After I managed to get this HP working I decided its time to buy a power supply tester. from Tigerdirect.com
HP Pavilion Elite m9426f Desktop PC Product Specifications
The HP Elite is really cramped for space inside.the case becareful, are you may disturber some wireing.
I even took the one from the Elite and put it into my Computer to verify it was Dead.  We had a lot of Thunderstorms, Power outages this past Summer and Fall. It didn't work, there was a green light on the back though. My guess was right.
I still have a problem. I need to know why the PS light is Green and The MB light was on. I'll do that when I'm Bored. I still have the Dell Dim 4500 to repair. And a Radio Shack Karaoke Player, whose CDG player keeps going IN and Out (Eject) with the power on. And with the Power plug unpluged from the wall socket, if you pull put the CDG tray and push it in, the Power On --Off switch RED light comes on as  your moving the tray in and out. Batteries not included.
I followed the above link HP Guide except for replacing all the Computer parts. One at a time as they suggested.
The HP Elite case  is tight inside not much space for big hands, Some people have asked if they can change the motherboard . The answer is Yes and NO.
It depends on if your going to install a manufactures replacement or pick a upgrade from TigerDirect.com or install one from another Computer. or if your having problems with the Computer you have.

The HP Elite m9426f I worked on had a bad power supply and wouldn't bootup. althogh the power supply had a light on in the back that was on indicating it was working.
I installed a new power supply after putting a test power supply in the computer .

If you just love the HP Elite and you know the Motherboard is bad then see if HP has a replacement. or call ASUSTech and see if they have one for a HP Elite m9426f . I would have to know why you want to change your motherboard.
The HP Elite I worked on had a good CPU, lots of memory, all the whistles and bells you need for most modern gaming and office work or everyday internet surfing.
If your wanting to upgrade to a faster machine that will do the new games and Windows 7 or just tweet
or all of the above, you have one now, the HP Elete
m9426f will or should do it all. The reason a computer slows down is mostly because you need to do a clean up of the Hard Disk Drive, and Clean the dust and dirt from inside your Computer. The other thing is how do you Connect to the internet. Dialup, DSL, Cable or other.
My thoughts on the future of Computing
The Computer we know today will be gone, the computer 20 years from now or less will be small to large like you TV's, however they will be completely diffrent then we know them today.
Tomorrows Computer, TV, Phone, will be Holograms  all into one.. Beam me up Scotti.

It will look like a folder that you put, your school work into, and opens with the light green up against your wall in your home and the darker greens on your floor. and would be called  Hologinnics 180 or be a Circle Hologinnics 360 or something like that with the 360 you pay more.  you know manufactures marketing people.Having fun yet ?
The Hologinnics will be about 1/4 inch to 1/2 inch thick, and contain all your electronics, and all your add on will be wireless. All you have to do is open it up and place it where you want it. Thirty years from now it will be a laser light beaming from your ceiling.
Your  virtual keyboard will be visable on your
Hologinnics and you will use the virtual keyboard to operate your electronics, don't believe me, try this go to START then RUN, type osk.exe. see what you get. most geeks know this allready.
A co-worker friend of mine lost his hand and he had to answer a lot of emails from his boss, I told him to do the Start, Run, OSK.EXE he was happy about that then bought Dragon Natural Speaking latest addition came out and he purchased it.