New hard disk not recognised [Solved]

[Keith]

My PC has died.  RIP. 
I have resurrected a very slow 1998 PC and was surprised to be able to load it with Ubuntu V12, so at least I can tell you about it.  Slowly.
I discovered that the hard disc from the dead PC had a mechanical fault, but by holding it at just the right angle was able to copy the files to the 1998 PC via the USB.  I then bought a new Western Digital HD and fitted it to the dead PC, expecting to be able to load Ubuntu easily. 
Ha!  Not even a POST display.  The VDU is fine; I've replaced the PSU; replaced the 3V motherboard battery; and shorted the BIOS reset pins as per the manual.  Not a dicky bird.  I would be grateful for any ideas, short of buying a new PC. 
The motherboard is an ASRock 775i65G. 

[SeZo]

Is there power on the MB? Any led's lit up?
Does the fan starts on the processor heatsink?

[Keith]

Thank you for your reply.
Yes:  all the lights are on and the CPU fan is working.

[Mark Greaves (PCNetSpec)]

Unplug everything that's not necessary to get a POST screen.

eg. HDD's, CD/DVD's, floppy, card readers, add in graphics card, etc.

connect to the onboard graphics adapter

Does it POST ?

if not also remove the RAM .. does it beep when turned on without RAM installed ?

[EDIT]

The BIOS reset isn't still shorted is it ?

[Keith]

No, the BIOS is not shorted. 
I disconnected everything and when the RAM is removed, there is a repeated sequence of three beeps.
Still no POST.

[Mark Greaves (PCNetSpec)]

Did you also disconnect all external devices such as mouse and keyboard ?

Have you tested the monitor on another PC ?

Have you connected the square 4 pin lead from the new PSU to the motherboard ?

have you got an add-in graphics card you can try ?

[Keith]

Did you also disconnect all external devices such as mouse and keyboard ? 
Have you tested the monitor on another PC ? 
Have you connected the square 4 pin lead from the new PSU to the motherboard ?
Have you got an add-in graphics card you can try ?

Mouse/keyboard:        Yep: nothing but the monitor connected.
Tested the monitor:     Yes: it's the one I have to swap between the dead one and this slow one.
4-pin lead plugged in:      Yes, I have - I just copied the connections used by the old PSU.  Perhaps I ought to try the old one again.
Add-in graphics card:  I removed it for the other tests but shall try it again and report the result.

[Edit]
Replacing the add-in graphics card had no effect.
The PSU comes with two 12V, 4-pin leads so I changed them over, replaced the memory and - Hey Presto!  The BIOS demanded that I select a valid boot device. 
I shall persevere and report back.  Thank you for your advice so far.

[SeZo]

What were the simptoms of the (original configuration) PC dying?

[Mark Greaves (PCNetSpec)]

OK, bung it all back together and see what happens

[Keith]

You can't beat a good bung!   (Shades of Silvio Berlusconi) The system is now up and running with V12 installed.   
I would be surprised if changing the 12V lead was really the problem as the PSU is brand new, but I guess I just needed the impetus of your suggestions to keep waggling the connections!
My thanks as ever for everyone's generous help - sorry if I've been wasting your time.

[Mark Greaves (PCNetSpec)]

There's no guarantee that both 12v leads are working .. but whatever it was, I'm happy to hear it's now solved

[Keith]

Ah, that's interesting!  I shall check it when tidying up all the kit.
Thank you, Mark.