Step 1 is the fuse. According to my handbook, it's actually behind a panel in the glove box (20Amp standard blade) - a block of six, and it should be top left - rather than the main fuse box.
(ETA: It is most likely a blown fuse)
Step 2 is to check the motor, for which you will need a multimeter and a mate. (i'm doing this from memory, so it may be slightly wrong). Access the roof console, disconnect the wires from the motor and connect in the multimeter (set to voltage, 20V or more). Get your mate to start the car, then press the sunroof button. If you don't get a voltage, you've got a wiring problem. If you do get 12V, then either the motor's dicky, or the mechanism's jammed.
Step 3, check the mechanism. Tip: Do NOT try this until you think it's the problem - the mechanism is "keyed", so if you set it wrong the sunroof remains part-open, or tries to force itself extra-shut. Which is a pain to get right again, especially if it's about to rain. (guess who learnt from experience to check for a fuse first!)
Inside the roof console, you will find a spanner key. this plugs into the motor, and manually works the sunroof. Turn the key and check that the sunroof actually opens reasonably freely. If necessary, regrease.
If these all fail, it's likely to be the motor, so you're looking to visit a scrappy. I didn't get this far, so i can't tell you how easy or difficult it may be to replace.