SIMPLE PRESENT:

Statement:
--They accept credit cards.
Question:
--Do they accept credit cards?
SIMPLE PAST:
Statement:
--They accepted credit cards last year.
Question:
--Did they accept credit cards last year?
When using did in a question, the main verb will be in the infinitive form, not the simple past tense.
NOTE: For a negative question in the past, use didn't.
--Didn't you get my letter?
--Didn't they come?