I have a inspiron 6400 which I retreived from ex wifes trash can, she said it was beyond repair and I was waisting my time but I am typing this from it. she had used a external mouse for over a year and I could only get the mouse to work very little if at all. I tried everything with no luck until one day my fingers became pinched by the screen casings and I noticed "all" the screws holding the screen casing had become loss. Being a heavey equipment mechanic for twenty years I read the section of the owners manual covering disassemble of this laptop  and remembering where I found the laptop, "trash can" that I would not be ot much if I destroyed it. I removed the screen from base or key board section and found that the hinge screws had backed out as well, I put a drop of super glue on the screws "as' I tightened them and that was six months ago and the touch pad has worked with not one glitch. My ex  wife had run this laptop for so long with the fan almost completely plugged that the base or key board section is warped 3/16ths from over heating and I have dropped it from over four feet more than once and I would buy another dell because this one has been to hell and back and is still working excellent.

as I stated above that the screws had backed out so look at yours very close when you open it to see if there is any movement and or put one hand on the top edge to feel any movement when the screen is opened. If you see or feel movement between the cases take yours to a pc shop or send it back to dell if still covered by warranty. My dell is opened and shut no less than twice a day and sometimes alot more but I do not blame dell for a design flaw that was missed in the R&D stage of development although they might look into running a seperate ground wire and not depend on the screen casing for the ground. one more thing, move the screen back & forth while moving the touchpad cursor and see if the screen movement affects the cursor then you have the same problem as I did. hope this is helpful.