If you are looking at daily data (X number of hours of trading compressed into one data point) and the "open, close, high, and low prices are the same" then:

(1) The stock did not trade that day

(2) There was only one trade all day which then meets all conditions (O, H, L, C)

(3) You are getting bad data

If there is a volume number in your data, it will distinguish (1) from (2).

If you are looking at daily data (X number of hours of trading compressed into one data point) and the "open, close, high, and low prices are the same" then:

(1) The stock did not trade that day

(2) There was only one trade all day which met all conditions (O, H, L, C)

(3) You are looking at bad data

If there is a volume number in your data, it will distinguish (1) from (2).