You'll see a chart in the data sheet for the HT12E and HT12D that shows how to select
oscillator resistor values.

I normally use 33K for the decoder when operating at 5 volts. Locate 5 volts on the
bottom of the chart in your HT12D data sheet, and follow the vertical line up to where
the line from 33K on the right crosses it.

This indicates just a tad >200kHz internal oscillator speed at 5 volts with 33K.

Now look just below the chart where it states The recommended oscillator frequency is
fOSCD (decoder) should be about equal to 50 x fOSCE (HT12E encoder).

Now follow the vertical line up from 5 volts in the HT12E data sheet to where the line
from 750K crosses. Just short of 4kHz.

With +/- 5% resistors, you're in the ball-park.

If you have a scope you can experiment a bit with oscillator resistors to see the effect
changing them has on the encoder data output signal.

At any rate, if you're getting nothing on the data output pin of your HT12E when /TE is
at ground, then I would suspect you have a bad encoder.