Where have my endless hours of grinding go?
When did you last log in to the characters?
http://classic.battle.net/diablo2exp/faq/realms.shtml
What are the character expiration rules?
Diablo II Battle.net Characters track their own expiration status. For example, the character selection screen will show an expiration period of 10 days for any newly created character. Once you log two hours of in-game time on that character, the expiration indicator will disappear. If you play the character for less than two hours total game time, then you will continue to see an expiration indicator on your character selection screen. Each time you log into that character, the expiration indicator will show 10 days until you accumulate a total of two hours of game time. If the character does not have two hours of game time and is not played for 10 consecutive days, it will expire and we will not be able to restore it.Once the character has logged two hours of total game time, it is considered an active character. If this active character is not played for three months, it will expire. After one month of inactivity, a new message will appear displaying a 60 day countdown before the character will expire. Once the character is played in a game, the countdown will once again be reset to three months and the expiration message will no longer appear. Be sure to keep your characters active by playing each of them in a game at least once every three months. We are not able to restore expired characters for any reason.