check your serial cables first of all- always.
there is no 'standard' connector sex or whatever- or pinouts that should be connected for rs232-
sometimes tx is labelled as rx, sometimes vice versa. sometimes with respect to 'modem' device, sometimes with respect to 'computer'.
the manufacturers of rs232 devices never even managed to use a consistent connector sex to indicate the usage of the serial port either.
is there any other way to control this projector? www? ethernet?