I had opened up my MacBook to replace my optical drive with a SATA cable so that I could connect my external SATA drive internally and get the speeds that I need. After opening the case so many times, I guess the cable just broke. This being the case, my trackpad and internal keyboard no longer functioned, and I had to go about a week using a 10 year old Apple Keyboard and Mighty Mouse. This was very cumbersome and awkward, as I am a college student and use my laptop for lectures.
The repair went very well. All I did was take out the top, take off the old cable, put the new cable in (making sure that picky connector connecting the trackpad was really in well), and then put the top back on. Keyboard and trackpad (and power button) now work perfectly like nothing had happened.
If you are a techie like me, you will have no problem performing this (or almost any) repair. If not, be sure to take a look at the guides on how to handle opening your case as you have to be careful not to break anything.