What can you do if Harvey Norman takes a ridiculous amount of time to fix a computer under warranty.?

There has been a problem with a computer i bought from Harvey Norman a while ago. I have taken it in for repair a few times and most of the times they return it to me within a few weeks. On the terms and conditions, it says that repairs may take up to 6 weeks but my computer has been in the shop for about 9 weeks. Is there anything i can do? can i complain and can i be compensated for not having the use of my computer for almost a month longer than what was stated in the terms and conditions.