This manual is for the XPS14z and may NOT be the pc that you have. This does give pictures and descriptions of the hall sensor.

Hey there, I've managed to remove it but I wondered what it actually is/does

Here is a wikipedia article explaining it.

en.wikipedia.org/.../Hall_effect_sensor

I am just guessing:

It is possible that the hall sensor is used to shut down (or whatever your settings are) the system when you close the lid.My inspiron 1545 doesn't have a hall sensor entry in the device manager but I can shut down my system by using a magnet and holding it close to the right side of the touchpad.If I use a screwdriver or something else that can be magnetized I can locate the system's magnet at the upper rim of the lid.My guess is that on my mainboard a tiny reed relay (a mechanical switch that moves its contacts when exposed to a magnetic field) is activated as soon as the lid is close enough to it.I can use this "feature" to pretend to be a magician ... ;-)

You wrote that you "removed" the sensor - might have been not a good idea.Test the functionality of the lid.

Ooh right thank you and the sensor was causing the laptop to malfunction and not boot. As I've said the wires are melted on it (and I'm not sure why as it's 2nd hand) but now I've removed it it boots fine.

Oh yes - missed the "melted" part.Of course to remove the sensor/cable was the right thing to do and if the sensor was used in connection with the lid I wouldn't call it a tragedy to live without it....... ;-)