bought the UK Collector's Edition... i already heard that there were issues with faulty Mac/PC-only prints, so i feared that there was a chance of getting one of those.
Yep. Your fears are confirmed; you got one of the bum disks.
Read through the
Official Mamba Games Retail Machinarium Thread for the whole story.
Or - if my guess is right and it's specifically the PC version that you're missing - just write to:
support@lm-global.net and remember to include some form of proof of purchase to expedite the process.