seatbelts wont work

[Act]

when i bought my car, i noticed that both of my seat belts dont work, by that i mean they dont slide when u open or close the door, would anyone know why? i checked the fuses and everythings kool.

[casterX]

check or replace the "brain" of the seatbelst.. it's under the front passenger seat..

[Act]

ok kool, how exacly will i know where it is or how can i recognize it?