[Dilettante_Pro]

Либо так

A<input id="data_a-gwert" type = "text" value = "1"> 
B<input id="data_b-gwert" type = "text" value = "1"> 
<input id="data_v-gwert" type = "text" disabled> 
<table>
<tr id="block_5000" >
<td id="block1_5000" >тест</td>
<td id="block2_5000" >тест</td>
<td id="block3_5000" >тест</td>
<td id="block4_5000" >тест</td>
</tr>
<table>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$('#data_a-gwert, #data_b-gwert').on("input",function(){
   $('#data_v-gwert').val($('#data_a-gwert').val() * $('#data_b-gwert').val()) ;
   if($('#data_v-gwert').val() <= 5000){
$("#block_5000").css ("display", "block");
}
else {
$("#block_5000").css ("display", "none");
}
});
</script>

либо так

A<input id="data_a-gwert" type = "text" value = "1"> 
B<input id="data_b-gwert" type = "text" value = "1"> 
<input id="data_v-gwert" type = "text" disabled> 
<table>
<tr id="block_5000" >
<td id="block1_5000" >тест</td>
<td id="block2_5000" >тест</td>
<td id="block3_5000" >тест</td>
<td id="block4_5000" >тест</td>
</tr>
<table>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$('#data_a-gwert, #data_b-gwert').on("input",function(){
   $('#data_v-gwert').val($('#data_a-gwert').val() * $('#data_b-gwert').val()) ;
   if($('#data_v-gwert').val() <= 5000){
$("#block1_5000").css ("display", "table-cell");
$("#block2_5000").css ("display", "table-cell");
$("#block3_5000").css ("display", "table-cell");
$("#block4_5000").css ("display", "table-cell");
}
else {
$("#block1_5000").css ("display", "none");
$("#block2_5000").css ("display", "none");
$("#block3_5000").css ("display", "none");
$("#block4_5000").css ("display", "none");
}
});
</script>