This is almost certainly Farligt venskabFarligt venskab. The cover art alone should trigger your memory if this is the right one - it's a big machine with black colored metal parts strapping the boy in.
Frankenstein meets Big in this well-made thriller created for the computer generation (the film's subtitle is Password to Life). A dying physician (Ulf Pilgaard) changes bodies with a healthy but shy and socially inept teenager (Morten Schaffalitzky), who then spends the remainder of the film attempting to convince his dubious friends to help him get his body back. The film features comedian Ulf Pilgaard in a rare serious role (in Nattevagten [1994] he did his mad doctor bit so well that he won the Danish equivalent of the Oscar). Directed by actor Jørn Faurschou , Firelight Veins rather successfully straddles the fence between teenage angst melodrama and action-packed science fiction. ~ Hans J. Wollstein, Rovi
Trailer