I have an emachines t6520 and the power sw wire, HDD led wire, and the power led wire hve been disconected

Most Motherboards are made to only accept certain plugs in that specific spot! If you are trying to add something new like a new Fan or LED, or HHD and you need power you would have to use a 4 prong plug off the power supply, If your power supply does not have any more available plugs, Amazon.com or Newegg.com sells splitters!

Good Luck and Best Wishes!

H57H-AM2 v2 Motherboard in a Gateway DX4840 wire connections for Front Panel are shown here in Photo. I took them before I disconnected mine so it works.

it should be printed on the motherboard itself. if not, go google emachine t6520 front panel connections.

The manual for your computer is available from emachines, p.168 shows the info you need (replacing the front I/O panel)
http://downloads.emachines.com/userguides/8511279_eM_NG3_chassis_HW_ref_en.pdf

The good news is that you can't harm the computer by connecting the wires wrong and the bad news is they just won't work the way they are supposed too if not connected properly. The LED's must have the correct polarity to work.
In general, if you look real close (as in magnifying glass and flash light) you will see the ID for each set of pins is printed on the motherboard (pwr,rst,HDD,pwr sw,speaker) Just match what it says on the motherboard to what it says on the wires. Don't worry if you get the polarity wrong. If a light doesn't work just swap the two wires. The colored wires should be positve (+), though. The reset (rst) and power switch (pwr sw) wires don't require polarity.
These instructions are for most computers in general, YMMV.

There are may motherboards, but most have writing on them as to what is suppose to plug where. For example, for the power switch, the lettering might be "Pwr" or "Power" or "Pwr sw". The pins are usually together and should fit the plug on the end of the wire.

open up you pc case...mind out for static! dont touch what you dont have to and look for a printed ( normaly white ) motherboard model id..this might be the name of a manufacurer or just a few letters and numbers plus a revision number at the end. armed with these, trot of to google and stab them in. you should see a host of sites, but look for one that is the support site for your board...track down you board on the support/download site and there should be a manual & drivers ect to help you :)

The motherboard in your computer is an MSI MS-7145, which is also called RS480M. You can download a copy of the manual here. The front panel connections are on page 2-20.

Looking at the header JFP1, pins 1 through 9 (odd numbers) are the front row, pins 2 through 10 are the back. Pin 10 is the missing pin. The power switch connects to pins 6 and 8. The power LED connects to pins 2 and 4. The HDD LED connects to pins 1 and 3. The reset button, if used, connects to pins 5 and 7.

check on the motherboard there should be a small prints on it near control panel.

see to the front panel section on mother board possibly on the right hand side of bottom u can see the label there to connect hdd led

these normally go at the front of the motherboard if you are looking at it where the power supply box cables are at the back. There are litlte pins that these fit onto that will say on the motherboard Hdd led etc... in small writing.

hope this helps