Right here at HP Support,
1) Motherboard Specifications:http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00361570&tmp_task=prodinfoCategory&cc=us&dlc=en&lang=en&lc=en&product=459491
Scroll the page down to the top view illustration, and photo.
A) The motherboard uses a 24-pin ATX main power cable.
In the illustration the connector on the motherboard is on the right side.
It is an empty rectangular box with ATX Power Connector in it.
On the motherboard photo it is the rectangular white connector with two rows of 10 socket holes, and is to the bottom right of ram memory slot 2.
Another example of a 24-pin ATX main power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24
Ensure that the 24-pin ATX main power cable's connector, is locked into place on the motherboard's connector. The lock tab on the main power cable must be hooked over the tab on the motherboard connector. This ensures that the main power cable is in all the way.
B) The motherboard uses a 4-pin ATX +12 Volt power cable.
The connector on the motherboard is a white square connector, with 4 socket holes.
In the illustration it is to the bottom left corner of the Processor socket (LGA 775), and has ATX12V underneath it. This power cable's connector also has a lock tab.
Another example of a 4-pin ATX +12 Volt power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
Power TO the motherboard, that's it.
Power FROM the motherboard:
C) System Fan, and CPU (Processor) Fan.
Abbreviated as SYS_FAN, and CPU_FAN to the bottom left of the ATX12V connector.
(4-pin ATX +12 Volt connector on the motherboard)
The System Fan is the computer case fan.
CPU Fan is the Processor fan.
D) The four SATA headers on the bottom right in the photo, (Blue, Orange, Black, and White), are for the SATA data cables.
They connect to a SATA harddrive, or SATA optical drive. (CD/DVD drive)
(They are an L shaped connector inside, with 7 pins inside)
Power for these SATA devices comes from the Power Supply.
The Power Supply has SATA power cables.
Example of an average SATA power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#sata
(L shaped connector with 15 pins inside. The longer connector between a SATA data cable, and a SATA power cable )
Did you forget which SATA data cable plugs into where, on the motherboard?
Don't sweat it.
The beauty of SATA is that you can plug the harddrive's SATA data cable into ANY of the SATA headers (Connectors) on the motherboard, and BIOS will find it.
Same with a SATA optical drive, or any SATA device, for that matter.
IF, your SATA harddrive has a place on the back for BOTH, a SATA power cable, and a 4-pin standard Peripheral power cable, ONLY use the SATA power cable.
Using both will eventually burn out the SATA harddrive!
Example of a 4-pin standard Peripheral power cable, (Misnomered as 'Molex'),http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
From there the main optical drive, (CD/DVD drive), has to have the audio cable plugged into the audio connector on the motherboard.
(Plus the power cable, and data cable, of course)
In the illustration this is the header down in the very far left corner, and located towards the bottom edge.
It has CD_IN marked underneath it.
In the photo it is the Black rectangular connector in the very far left corner.
If you didn't connect the 4-pin +12 Volt power cable, your Processor isn't getting any power.
No Processor operating, No computer.
No Signal on monitor.
(No video signal)
For additional questions please post in a Comment.