If you are a first year then having a low attendance at this point in the year won't have led you to being kicked out, but stealing stuff probably will do so.
- You say the timetable's are only available online, so get print outs of them and if they don't add up then take those print outs to your tutor and insist he/she helps you with them.
- The lecture you went to and were told you were not registered for it. Was it the correct lecture (given the timetable issues)? Did you actually confirm this, not necessarily with the lecturer but you could have asked someone else attending the class. Did you go to the appropriate faculty office and find out why you did not appear to be registered for that particular lecture series ... not a general "I don't seem to be registered?", a specific "Lecturer X has told me I am not registered for Class Y, please can you check this".
- Did you actually even go through the registration process for the course, not the acceptance of the place through UCAS (or whatever ... it's been a while since I was an University) ... but the actual registration at the University at the start of term?
- Regarding the stolen hard disk? First simple question is, of course, did you do it? If not, have you been in the room which it was stolen from? have you used the machines in the room in question and could have left yourself logged in (and hence appeared that you were present when it was stolen)? Could someone have seen your username and password and hence have been logged in as you in the room at that time? That room doesn't have a swipe card entry system does it and you've lost your card? What were you doing at that time and can you prove that?