- Events don't generally disappear by themselves and making events go away requires you to press the delete key while highlighting an event / go to Edit > Delete which you would recall doing. What happened right before they disappeared?
- Are you using iCloud and if so, do your calendars show up when you look on www.icloud.com?
- Do you backup your computer to an external hard drive or have some other kind of backup of your data? (http://support.apple.com/kb/HT1427)
If you've already made sure that all your calendars have a check mark on the left hand side and you are looking at dates / years when you know there should be events there are only a few things left to try:
1. Go to iCal > Quit iCal
2. Remove the following to the trash and restart your computer:
Home > Library > Caches > com.apple.ical
Home > Library > Calendars > Calendar Cache, Cache, Cache 1, 2, 3, etc. (Do not remove Sync Cache or Theme Cache if present)
Home > Library > Preferences > com.apple.ical (There may be more than one of these. Remove them all.)
--- NOTE: To get to "Home > Library" in Lion: Click anywhere on the desktop and then click on the "Go" menu at the top of the computer screen while holding down the "option" key on the keyboard. You will see "Library" in the menu.
3. Launch iCal and scroll through the months to look for any events.
If the events are still not visible then I only see 3 options:
1. Restore your calendars from a backup if you have one (If you don't make backups of your computer now would be a good time to start http://support.apple.com/kb/HT1427.)
2. Re-enter your events (Start backing up until you know what caused them to disappear. Even if you don't have an external drive you can still at least make a copy of your calendars on your computer for safekeeping:http://support.apple.com/kb/HT2966 )
3. Use data recovery software or a data recovery company to scan your computer for iCal events (.ics files):
Data Recovery Software:
You can contact a local Apple Authorized Provider to see if they offer data recovery services: http://www.apple.com/buy/locator/service/
There are many nationwide / worldwide data recovery companies out there. Here are a few examples:
Best of luck to you.