after importing calendar, iCal not responding

I really messed up this time. I backed up my large personal calendar as am .ics file and then deleted my iCal calendar on all my devices and iCloud. I then reimported my personal calendar (9.2 mB) only to discover that iCal takes an hour to import the file and then suddenly goes into Importing iCal data continuously. When I do force quit, it says that the iCal is not responding anymore. I need my calendar and now I seem unable to import it? My iMac is circa 2006. Running Lion.

What can I do to recover my calendar?