My power LED cable from the case is too short to reach the mobo. How can I lengthen the cable? Any help is appreciated. Thank you.

just cut the connector off the end of the cable and connect two longer wires to the existing wires, and put the connector on the new end.
 
{}=====================LED
 
{}==========/   /========LED
(cut cables)
 
{}=========/ ======================= /==============LED
(add two new wires)
 
{}================================================LED
(use wire nuts/solder/electrical tape to bond the wires together.)
 
easy as pie.
which is not easy for some people...
but still, this is easy.

You just need some extra wire of the same size, and some electrical tape.   I would do what is referred to as a j-hook on the splices. Simply bend the exposed wire so that it forms the letter J. Then hook the 2 together, and twist. It is best that you solder this joint, but not necessary. Once you are done, simply cover with a few wraps of electrical tape.

That's unusual.  Check to see if it is hung up on something.  Last year I got a case on which the front panel screws on.  The drones who assembled it put a screw through the power switch wires.
If that doesn't help, buy a roll of 22 gauge stranded "hookup" wire.  Cut the two wires of the LED cable at least a couple of inches from the connector. Strip 1/2" of insulation at each end and splice in long enough pieces of the hookup wire to reach.  Cover all the connections with electrical tape.

Thanks for the help.

If you don't want to make one for yourself, you can order an extension cable:  from frozencpu.com  http://www.frozencpu.com/products/ [...] d=hJpVZ2ZY

 
I dunno... costs Price: $1.99      
 
If it were me i would order it, its the lazy way.