Tony,
Is yours an Auto or Manual?
Hate to be tempting fate, but look at my post about 'TD4 auto, no drive whatsoever'
This started with the fans being constantly on, and, they do run at three I think it is, speeds relevant to the computer saying what it needs.
In my case, Fuse Number 4 was the initial culprit!!
Worth a look??
Duke of Offley