Sat Nav showing wrong location...

[Smudge_si]

Hi

i have a mk 3 sat nav unit in my 02 x5 , the drive had recently crashed and left me with the blue "safe" mode screen . i have reinstalled the software and all is ok apart from i put the maps disc back in the unit and it wont find my position and when i manually add my location once i start driving it continues in a straight line in one direction . i am not sure where the gps reciever is or if i can replace it or even if that is the problem ?

thanks for any help
Si