Agree with StephanSA, and would like to add if I may.
It 'sounds', (Looks), as though you are trying to provide remote assistance to someone in Europe.
IF, this is in reference to an HP Pavilion P6370t desktop computer,
1) As stated there is one power cable coming from the Power Supply, to the motherboard to check.
There is another one also.
They have a Lock on the connectors, but due to shipping may have come loose.
A) 24-pin ATX main power cable.
Typical example,
http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24B) 4-pin ATX +12 Volt power cable,
http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4Photo of the bare motherboard with no power cables plugged in, or hardware attached,
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c02014355&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&site=null&lang=en&product=4124612&key=nullGive the page a few seconds, the motherboard photo will come up.
Look to the right of the board. (Motherboard)
See the whitish connector that has two rows of 12 socket holes?
This is where the 24-pin ATX main power cable, plugs in.
To the left of the Processor socket, is whitish square connector with 4 socket holes.
This is where the 4-pin +12 Volt power cable plugs in.
Also make sure the SATA power cable is plugged in tight, to the SATA harddrive,
Example,
http://www.playtool.com/pages/psuconnectors/connectors.html#sataMake sure the SATA data cable is plugged in tightly to the SATA harddrive, and into the SATA connector on the motherboard.
On the motherboard there are two SATA data headers, (Connectors) One is Orange, one is Blue.
(Below the Ram Memory slots)
Also you can click on the + sign next to > Motherboard Layout, and view an illustration of the motherboard.
ATX1 is the connector for the 24-pin ATX main power cable.
PWR1 is for the 4-pin ATX +12 Volt power cable.
SATA4 and SATA3 are the SATA connectors (Headers) I referred to.
Also make sure the Processor fan cable is plugged in tightly to the motherboard.
CPU_FAN1
Where it states JFP1, this is the header (Connecting pins) on the motherboard, that the cables, (Wires) from the Front Panel connect to.
The Front Panel is the front plastic part of the computer, that has the Power On button, and etc.
Be sure it is plugged in tightly.
Most of the time it is that the Ram Memory modules, ('Sticks') have become loosened.
Remove all Ram Memory modules, reinstall them.
NOTE*
BEFORE starting!
Computer unplugged from power. Computer on a table, computer case open.
OBSERVE Anti-Static Precautions.
Anti-Static Precautions:
Your body carries Static electricity.
Static will fry out, (Short circuit) the hardware components inside a computer.
You may not even see it, or feel it.
Computer unplugged from power, computer case open, TOUCH the metal frame to relieve your body of Static.
Should you leave your computer in the middle of working on it, be SURE to touch the metal frame again upon your return.
(Unpainted surface)
None of this works? Post back in a Comment, and we'll go further.