Christ, could be a whole host of things.
I suppose the obvious and easiest thing to do first would be to check all the wires going to alternator, starter motor, battery, all the sensors. Just give it a check over to make sure nothing is out of place.
Then I suppose it would be onto the gearbox. Get under the car and make sure that's still all connected up as it should be, driveshafts still in, no bolts loose or missing. I'd be inclined to say to take off the gearbox and inspect the clutch aswell, but when you say the car wont even try to start it's a bit worrying.
Do you get any dash lights come on?
Does it tick when trying to start it up?
Does it turn over at all?
Does your clock LED flash when you get in and put ignition on?
Do you hear the fuel pump prime up when you put ignition on?
Are your pedals still ok (clutch pedal still go down as normal)?
You need to get out to it and do some more investigation work
