The Acer Aspire E500 Desktop PC uses an Acer MBP2207024 motherboard,http://www.ascendtech.us/acer-aspire-e500-mbp2207024-motherboard_i_mbacembp2207024.aspx
I'll be referring back to the photos of the motherboard, at the bottom of the page of the above link.
Start with the power cables coming from the Power Supply, to the motherboard.
1) 24-pin ATX main power cable, and corresponding connector on motherboard:
Middle and bottom photo. Look at the top left side. There is a whitish long connector, with 24 socket holes in it, on the motherboard.
Here is an average example of the power cable, and the connector on the motherboard,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24
[Note* Color of connectors does Not matter ]
2) 4-pin ATX +12 Volt power cable:
It's hard to see in the photos. Go to the bottom photo.
From the left side; look at the purple Keyboard port, and green Mouse port.
Go to the right to the blue VGA port. (15 socket holes. 3 rows of 5)
Now go to the stack of 3 ports to the right of the blue VGA port.
Two USB, then a Firewire port on top. Right behind this stack, is the square 4-socket hole, whitish 4-pin ATX +12 Volt connector.
Average example of motherboard connector, and corresponding power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
Note that on the male power cable connector, for the 24-pin power cable, and the 4-pin power cable, there is a Lock.
Shown more visibly in the middle photo of the above link.
This Lock acts like a see-saw on a playground. The top is squeezed in, and this action releases the hook at the bottom end, away from the tab on the female motherboard connector.
To ensure that these power cables are plugged in tight, the Lock needs to be in the lock position, over the tab on the female motherboard connector.
This power cable is power for the Processor.
That's it for the motherboard.
There should also be a SATA power cable coming from the Power Supply, to the SATA harddrive.
Average example of a SATA power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#sata
There are two cables going to a SATA harddrive. The SATA power cable has the longer connector. It has 15 pins. Note that there is also an L shape on the inside of the connector. Lines up with the L shape on the harddrive.
The other cable is a Data cable. (information cable)
It has 7 pins, and is the shorter of the two.
Average example of a SATA data cable, and corresponding connectors on a motherboard,http://en.wikipedia.org/wiki/SATA
Look at the photos to the top/right. The top photo shows an average SATA data cable. (Color does Not matter)
The photo also shows a Straight connector. This style of connector is usually used to plug into the motherboard. (Sometimes for SATA optical drives, also)
An Elbow shaped connector is usually used on the Harddrive side.
This is a 4-pin standard Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
Shown connected to an older IDE (PATA) harddrive. It is also used on optical drives, and to computer case fans sometimes.
IF, your SATA harddrive has a provision on the back for a SATA power cable, AND a 4-pin standard Peripheral power cable, ONLY use just the SATA power cable.
Otherwise the SATA harddrive will BURN up.
May not happen immediately, but I assure you it will happen.
In the middle and bottom photos on the Ascendtech link, the SATA headers (Connectors) on the motherboard, are Orange, and at the Top/Right.
There are 4 of them.
The beauty of SATA:
Next to the SATA headers on the motherboard will be silkscreened a figure. SATA0, SATA1, SATA2, and SATA3.
Or it may have SATA1, SATA2, SATA3, and SATA4.
A harddrive should plug into SATA0, or SATA1.
HOWEVER, the beauty of SATA, is that you can plug the harddrive into ANY of the four SATA connectors on the motherboard, and BIOS will find it.
The plastic front of your computer is the Front Panel.
The rectangular block of plastic with pins sticking up out of it, on the motherboard, that the wires from the Front Panel go to, is the Front Panel header.
Sometimes abbreviated as F_PANEL, or FP1, or PANEL_1.
Looking at the Top motherboard photo, it is the blue rectangular connector, at the Bottom corner.
In the Bottom motherboard photo, it is all the way to the Bottom/Right corner.
(Middle photo all the way to the right corner)
The CPU Fan, (Central Processing Unit, or also known as Microprocessor, or Processor for short), cable connects to the small 3-pin whitish connector, that is towards the top of the motherboard, and above the 24-pin ATX main power cable connector.
The System Fan, (SYS_FAN), or computer case fan, connects to the small 3-pin connector to the Right, of the 4-pin ATX +12 Volt connector, on the motherboard.
Front Panel header pinout to follow in a Comment.