Why My Page Rank Decrease ?

My Page Rank Has Been A 2 For A Really Long Time. I Have Not Gained Or Lost A Lot Of Links Recently. But Why Did My Page Rank Drop From A2 To A 0 ? My Page Rank Has Not Changed In The Last 5 Months. Why Did It Change This Week? Nothing Happened To My Website This Week.

Please Where Is My Mistake ? Answer Me Via Comment Or Add Me On  Yahoo Messenger My Id Imran _Cuc@Yahoo.Com