Dell Inspiron 3551 Unresponsive Touchpad

You can fix it by switching off i2c_hid and setting nopnp in boot parameters this way

1. Run

   sudo -H gedit /etc/default/grub

   In the open window edit line

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

   it should look this way

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i8042.nopnp"

   Save file and run

   sudo update-grub

2. Run

   echo "blacklist i2c_hid" | sudo tee /etc/modprobe.d/i2c-hid.conf
   sudo depmod -a
   sudo update-initramfs -u
   echo "synaptics_i2c" | sudo tee -a /etc/modules
   

3. Reboot.

Not sure if you already fixed this, but you will need to blacklist i2c-hid. So all you will need to do is open /etc/modprobe.d/blacklist.conf as super user and add 'blacklist i2c-hid' without the quotes towards the end of the file. Reboot and your touchpad will work.

source: http://trustdarkness.com/wordpress/dell-sputnik-xps-13-touchpad-settings-not-working-in-updated-ubuntumint/