Are you staring softly? If you stare at it, then nothing will happen. Getting into the theta-gamma sync is not something that is forced. It really is something that you “fall into”. Gaze at the line where the wall and ceiling meet. Since you’re just starting, let your eyesight go fuzzy, then back into focus. Drop your gaze to the wall so that the line is in our upper peripheral vision. then raise it so the line is at your lower periphery.
Also, as Verdanadi said, using something like the snow on the TV set helps. When I was a girl, and doing this, (not knowing what it was really), I looked at patterned carpet or wallpaper (which was in great abundance in those days). I let some parts of the pattern come to the front of my vision, then let them drop so others came to forefront. Something like that might help.
Also, try looking at a checkered surface. As a kid I used to do this in public bathrooms all the time, because I thought it was cool. You look at the middle of a square, and the lines around it will start to disappear. Then shift your focus to the lines, and the squares around that square will disappear.
But the key is to keep your focus soft. You’re not staring something down. You’re luring it out.