When I started my MacBook today, it started to show my MacBook's time to 1 Jan 2001. But after I connect it to internet it goes back to normal? Why does it happen? Does anyone know any specific reason. I am on 10.6.2
When you connect to the internet if set up in the Date/Time Preference Pane the computer will retrieve the time from a time server (in this case, most likely time.apple.com) and set it to the proper time. If the time is being reset to January 1st, 2001 you most likely have a dead PRAM/Clock/CMOS battery or something odd happening with your PRAM.
You can try resetting your PRAM but restarting and holding the Command-Option-P-R keys down until you hear the computer start up (the "bong" sound). If that fails to work you'll need to replace the battery which is easiest by taking it to a Apple Authorized Service Centre. These batteries normally last 7-10 years.
Most probably the cell that powers your MacBook's internal clock may have drained. When you connected to the internet, the operating system most probably updated the time using NTP.
This happened to me today because I am at a hotel and I had not yet bought internet... their WiFi server was redirecting all pages to their "purchase our wifi page" so I guess that includes time.apple.com ... Their server is probably set to Jan 1 2001 so when my computer tried to grab the time from time.apple.com it was redirected and got their "purchase our wifi" page's server's time...
This is why when you connected to the internet it went back to normal.