Appointments and events keep disappearing from iCal

I put appointments and events on iCal and they keep disappearing. The ones that were added up until a few weeks ago are still there, just not the newly added ones. They will be there for maybe a few hours or a day and then vanish. I'm not techie at all. Please bear with me. I have an old MacBook, that runs Mac OS X, 10.6.8 and desperately need help!