That 4 pin molex connector is still concerning me a little, as there seems to be another one floating free at the bottom left, is that correct?

Yes. One is free (black & yellow wires) and able to reach the connection at the top of the MB. The other one is connected closely to the main one that powers the MB (red, yellow, orange and black wires). It cant reach the top connection but does have 4 pin writen on it.

This connection varies between motherboards. There are some motherboards that won't boot without it, but mostly just provide additional motherboard stability. I'm not had much dealings with Asrock motherboards, but could you confirm that one is 4 pin?

Not too sure on the black and yellow connector. Like I said above the one connected to the main MB power line has 4 PIN writen on it. Here's a picture and also a link to my particular MB and PSU

MB:
ASRock Motherboard - Product - 939NF4G-SATA2 - Overview

According to my MB instruction manual the connection with the black and yellow wire currently in is ATX 12V Power Connector. Further on it reads "Please note that it is necessary to connect a power supply with ATX 12V plug to this computer. Failing to do so will cause power up failure".
I dont get power up failures so I presume the wire in there is OK????

PSU:
Arctic Power 700W PSU - With PCI-E, SATA, 20+4, ATX12V, 8pin +12V Connectors - Retail Boxed - Ebuyer

PIC OF OTHER 4 PIN CONNECTOR:



I've downloaded that program and will post the shot as soon as I can. Should the program run for a little while before I take the shot?
Or should I just install, run, take shot straight away?

Thanks again for the help madmonkey, much appreciated. Getting much further than I have been.

It's running fine, spinning 3300rpm according to BIOS screen and the speedfan program.

Madmonkey:

Here are a couple of screen shots of Speedfan. A slight fluctuation on the voltage readings.

OK, that 12v rail is looking a little low. It may fluctuate around the 12v value but not as low as 9v.

Can you try that other 4pin molex connector, than try speedfan again. Can you also tell me what CPU you have, Graphics card and the wattage it shows on the side of your Power Supply Unit? I'll calculate the required wattage for that PC to make sure they match up. I also need to make sure the high temperature warnings showing on Speedfan are correct, as these are different between CPU's. 53c seems OK to me unless you have an Intel Pentium 2 or 4.

Can you try that other 4pin molex connector, than try speedfan again.

The computer doesn't boot up with the other 4pin molex plugged in.

Can you also tell me what CPU you have

An AMD Athlon 64 X2 Dual Core 4200+Ghz (2.2Ghz x2)

Graphics card

nVidia GeForce 6200 TurboCache
GeForce 6200 with TurboCache

The wattage it shows on the side of your Power Supply Unit?

700w

hehehehe, 700w? Well... errr, slight overkill lol, I think that PC was built by Felix the cat! I'm under the impression that it has been pointlessly reworked too. That PC will run quite happily on a 350w Power Supply Unit, but that doesn't prove that the Power Supply Unit is the cause to all of your problems. The low voltage problems can often be a result of the motherboard, although from what I've seen of the Power Supply Unit, I'm starting to lean in that direction.

Do you have a multimeter, or a power supply from another PC you can test, possibly a friends PC (as long as it's 350w+)?

I have a standard ATX 500w that was originally inside the PC

PIC:


Do you have a multimeter

Nope

Or a power supply from another PC you can test

I could put the one above back if you think it'll make any difference.


I think things are leaning towards the motherboard, dont you think?

Here are some pictures of my graphics card. Not sure if it is an NVidia card as it has no nVidia branding on it at all. The chips say "ELIXIR".






It isn't a nVidia card either, well according to this google image search???
Google Image Result for http://www.hardware.info/images/old/reviews/000537-00.jpg

How can the computer say it is when it isn't?