Bibi,
Thanks for asking your question to planDisney!
Disney has a phone line you can call to see if a
ticket is still valid. Simply dial
(407) 939-1289. When you give them the ticket information, they can quickly let you know the ticket status. You can also ask at one of the Guest Relations offices at the parks, but clearly knowing before you go is preferable.
BONUS TIP #1Most tickets are sold without the purchase of the "No Expiration" option. So, if you bought the ticket after 2004 without that option, the tickets would have expired after 14 days from the first use. If you are at all unsure, it is still well worth the time to call and double-check, but I thought this might help you get an idea of the possibility that it was still active.
BONUS TIP #2For most older tickets you often will need to have Disney adapt them for current use. If you can, have an idea of how you might want to use that ticket going forward. Consider options like transferring the value to a new ticket purchase or opting for a comparable ticket. You may also want to have a future visit date in mind. The options that they can provide will vary but knowing what and when you would want to use that ticket will help in your conversations.
Have a Magical Vacation!
Doug