The schematics look fairly simple but there are many places where the flow of electronic information can cease.
In addition to normal circuitry your project includes radio transmitting, radio receiving, and human input.
You need to verify that each stage is working.
* Is the supply voltage within correct range? Is it dropping too severely when the module starts transmitting?
* Is the A-434 (with 4 pins) drawing proper current when it's idle? Does current draw increase when it's transmitting (as would be expected)?
* Is output coming from the HT12E chip? If not, then are your input pins really going low when you press a switch?
* Looks as though pins 15 and 16 are connected to an onboard oscillator. Can you observe a waveform? (Okay, so it may not be possible to make this test.)
* Can you use an RF detector (of whatever sort is handy) to verify that broadcast is coming from the antenna? Field-strength meter? Grid-dip meter? Homemade or otherwise? Buzzing in a high-gain amplifier whose only input is a few inches of wire close to your transmitter? Buzzing in a nearby tv which you set to receive air broadcasts? TRy the tv on different channels.
* Your project transmits on 430 Mhz. This is about twice the frequency of tv channel 13. You might pick up a subharmonic (or something like it) on an old/miniature tv with a variable tuning dial.
* Is proper supply voltage going to the other A434 chip (with 8 pins)?
* Can you verify expected voltage levels at the chip's output pin?
* Is any signal reaching pin 14 (marked 'DIN') of the final IC?
* Baud rates must match. If they don't then you won't get much in the way of output.
* Try a check for internal IC fusing by testing voltages at all pins. Not a good sign if you get midway voltage levels in a digital IC.
* Test for bad solder joints. Visually inspect with a strong magnifier. To test with a meter: With power applied to the circuit. Touch one lead directly to a pin, other lead on the trace leading to it. A bad connection will produce some reading. Don't use an ohmmeter on a setting that will send several mA into your IC which could ruin it.
* Assembling electronics components is often unforgiving of mistakes. When you apply power to a miswired IC, it can be ruined instantly. This is why it's a good idea to use IC sockets, so you can remove the IC's and check continuity of all paths on your circuit board with an ohmmeter.