help fixing a lexmark x4580 scanner unit?

basicly im in the office and my boss's scanner is bust, we believe the drive belt for the light has come loose from the cog and we cant get the sealed unit ((bit with glass)) to open, so far weve removed all the screwes we can and as far as we can tell its still held down by what i presume are plastic clips from the top casing, has anyone got any info regarding the sealing method for the casing on this scanner? i dotn want to pry a clip and find out it was a hidden screw! anyway any info would help thank you