If you can't find the serial number and you want to continue knowing what year, the only option I can think of, but it is something very dense, would be to search on Google for the model of the machine + some type of year that you think, for example 2001, if not It appears to search for the same thing but with 2002, and so on every year, I don't think it is so old that you have to search for many years. How long can it be at most? 20 years? It would be 20 searches, nothing more, good luck with the search