html/css/javascript button in the table doesnt work : 1. i put the button in the table, and it is automatically disabled!!
the button is not working , and i don't know why. help me!!

2. the second question that i want to ask is that i put the image in my button. and if i click the button, it want to change the image into another one. help me how to do it! 



<table border="0" id="seat_btn">
				<tr>
					<td><button class="btn" id="a1" type="submit" style="border:0px; background-color:white;" onclick="alert('a1눌렸어요')"><img class="btn-img" src="seat1.png"></button></td>
					<td><button class="btn" id="a2" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat2.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="a3" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat3.png"></button></td>
					<td><button class="btn" id="a4" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat4.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="a5" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat5.png"></button></td>
					<td><button class="btn" id="a6" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat6.png"></button></td>	
				</tr>
				<tr>
					<td><button class="btn" id="b1" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat1.png"></button></td>
					<td><button class="btn" id="b2" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat2.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="b3" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat3.png"></button></td>
					<td><button class="btn" id="b4" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat4.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="b5" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat5.png"></button></td>
					<td><button class="btn" id="b6" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat6.png"></button></td>	
				</tr>
				<tr>
					<td><button class="btn" id="c1" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat1.png"></button></td>
					<td><button class="btn" id="c2" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat2.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="c3" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat3.png"></button></td>
					<td><button class="btn" id="c4" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat4.png"></button></td>
					<td></td><td></td><td></td><td></td><td></td><td></td>
					<td><button class="btn" id="c5" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat5.png"></button></td>
					<td><button class="btn" id="c6" type="submit" style="border:0px; background-color:white;"><img class="btn-img" src="seat6.png"></button></td>	
				</tr>	
				<tr><td><button type="submit" value="1" style="height:100px;" onclick="alert('안뇽')">dfdf</button></td></tr>
		</table> 