How can I mount a TV when I can't find studs inside my wall?
If you have a wall, you have structure.

If your wall is masonry then the TV mount can likely be mounted directly to the masonry (or mounts are available which can).

If your wall is drywall then you must have structure behind it... perhaps your studfinder is malfunctioning or you're using it improperly?

Studs can usually be found beside original electrical boxes (as the boxes are mounted to the side of the stud). Check your stud-finder against both sides of a nearby electrical socket for functionality. If you cannot locate a stud, try tapping a small nail into the wall board near an existing fixture. If it meets resistance behind the wall-board then you have a stud. Wall studs should be spaced in regular intervals (usually 16" on center in the US) so you can simply measure over to your mount area to locate them.

Once you believe you have found studs simple repeat the above test: tap in a small nail to verify structure behind the wall board. Studs should be 1.5 inches wide, so check that you can mark both sides of the side (to mount into the middle).

You may need to tap many small holes to accomplish this without an adequate stud finder.