for data filling error fill the dropdownlist on when you open page. or do as per the comments of RDBurmon. now i am giving you solution how to use shortcut keys by using js.
<body onkeypress="HotKeyClick();">
<asp:button id="Btn" accesskey="x" xmlns:asp="#unknown" /></body>
in js add this js function
function HotKeyClick()
{
if(event.srcElement.type == 'text' || event.srcElement.type == 'textarea' || event.srcElement.type == 'select') return true;
var ArrButtons = document.getElementsByTagName('input');
for(var Count=0; Count < ArrButtons.length; Count++)
{
if(ArrButtons[Count].type == 'submit')
{
if(ArrButtons[Count].accessKey != null)
{
var keyChar = new String(String.fromCharCode(event.keyCode));
var acsChar = new String(ArrButtons[Count].accessKey);
if(keyChar.toUpperCase() == acsChar.toUpperCase())
{
if (ArrButtons[Count].disabled == false)
{
ArrButtons[Count].focus();
ArrButtons[Count].click();
break;
}
}
}
}
}
}