I just started having this problem and let me just say from the beginning that NO there was not any liquid spilled on the computer.
If i touch either button or the touchpad anywhere i get a loud BEEEEEEEP alarm that lasts about 5 to 10 seconds long. Sometime i see a msg CAPS LCOK N or CTRL locked. Other times i see nothing just the alarm. The next thing that happens is that the keyboard stops working after i touch the touchpad at all. If i restart the computer the keyboard will work fin until i touch the touchpad then it stops working. There are no Hardware errors in the Device manager. Everything is working fine. I have tried the update drivers for the items that i believe are the touchpad and they are all up to date.
If i plug in a mouse i can move around just fine. If i open Notepad and try to type nothing happens BUT if i touch the touchpad while active in notepad, the alarm will go off but then letters will show up in Notepad as if i typed something. Its like the computer thinks the touchpad is the keyboard. I just touched the pad and it gave me L\P;L]\\L i touched it in another spot and it gave me 00./L-P/PP;-L/LA.
I tried to disable the pad by going into device manager and after it was disabled i touched the pad and get the same loud alarm.
Since both keyboard and mouse pad are having issues and would connect via ribbons to motherboard, this is most likely your culprit, if under warranty talk to dell, if not, take it apart and reseat cables. If that fails, see if you can get a cheap mobo off ebay or time for a new laptop.