Please click on the mobility center button.( i.e. on the top right corner of keyboard you should see three button. and the one with two bolts icon ) , it should open a windows. There you should see the option to switch on the touchpad.
Also you can install the touchpad drivers from our support.euro.dell.com--enter service tag#--submit--drivers and downloads--select the operating system--and install the touchpad drivers.
Do provide us your system tag#, email address and name via private message,by clicking on my name in blue and then select send a private message