The h3ll you say.
Let me see if I understand this straight;
You unplugged THE harddrive to your computer..............
Then you plugged an old harddrive in, and expected to be able to use it.
Expected to because you've done it in the past.
1) Was it an old harddrive you had in the computer, removed it; and had a larger one installed?
2) Is it one that you have had in another computer?
Here's what I know, and why I'm asking;
When Windows is installed on a computer it assigns hash values, to certain major hardware components.
B) Motherboard: To include the motherboard chipset, and BIOS program. (To include version and date)
D) Graphics chipset
Change any two of these hardware components, and Windows will think it is being stolen. Put on another computer.
Microsoft User's License states, "One GENUINE copy of Windows per ONE computer"
(Microsoft makes one Master disk, and from it all GENUINE copies are made, and sold to the consumer)
Now if you stated you installed the old harddrive as a Slave drive; then I could understand.
That is a Power Supply power cable.
According to specifications the Harddrive is a SATA unit.http://h10010.www1.hp.com/wwpc/ca/en/sm/WF06b/12454-12454-64287-3328896-3328896-3658105-3687950.html?dnr=1
Internal Drives - Hard disk controller -SATA 3.0Gb/s NCQ SMART IV
The power cable to it is a SATA power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#sata
Probably what your P2, and P3 power cables are.http://www.ebay.com/itm/HP-DC5850-SFF-Motherboard-SPS-461537-001-/310417711958?pt=Motherboards&hash=item4846566356
P1 will be a 24-pin ATX main power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24
P5 cable, MAYBE, (Might be P3 too)http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
And P6 power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#floppy
This type of power cable is also used on a Card Reader.
A) SATA harddrive has to have a SATA power cable, and SATA data cable.
The SATA power cable's connector is wider, than the SATA data cable's connector.
15-pins for the SATA power cable connector; 7-pins for the SATA data cable's connector,http://en.wikipedia.org/wiki/File:SATA_ports.jpg
The above is a general example of a SATA data cable, and it's respective connector on the motherboard.
Your SATA data cable connectors on the motherboard, are of a different style than the above.
You have Four SATA connectors on the motherboard;
1) Light Blue
3) Dark Blue