The scissor frame has probably come detatched from the wooden outer frame. Without these side fixings the metal frame has nothing to lever against. Have a look underneath the chair mechanism, and you may find that there are 2 holes (one on each side) that require new fixing bolts. Use stainless steel nuts & bolts for best result. Another possibilty is that there are fixing screws missing from the footrest underneath.
Neilzmail, March 2008