Guyz I found the solution of the problem.... Yay.... So what I did is uninstalled archicad, java and QuickTime player from my laptop and installed them again. But this time I installed java and QuickTime player given with archicad tools... And BINGO... when I opened my archicad, it was working like butter once again.
So the problem was that, before I updated java and QuickTime player but since archicad was not compatible with the updated version and that's why it wasn't working perfectly. So I downgraded and installed them using the files given with archicad.
It took me a long time to sort it out but as we know "all is well that's end well"
I hope this small information will help others who may face this small and silly bugs.