Both the seatbelt and pretensioner have mechanisms. The pre tensioner should have a piece of braided cable about 5 or 6 inches long coming out of the top where it connects to the seatbelt. If it hasn't then it has deployed and will need replacing (£40 on eBay). The seatbelt has a mechanism that locks it in place when there is an accident. This can be reset turning it in to a standard inertia reel belt (£25 on eBay) or you will have to buy a second hand good one (£85-£100 on ebay). It should give you a light on the dash.
I can give you some help on how to change them. It's quite easy.