Textbox cannot get focused

Hi expert, I have the lines of code for the search box, but it looks like it cannot get focused sometimes. When users put the mouse insert in the textbox and just before type into the search textbox and when move the mouse away, the insert in the textbox is gone. How to fix the code below. Thank you!

<input a class="searchbox" onkeydown="if (event.keyCode == 13){var button=document.getElementById('BasicSearchButton');button.click();return false;}else{return true;}" name="searchKeyword" autocomplete="on"  maxlength="100" value="SEARCH" onfocus="if(this.value==this.defaultValue)this.value='';" onblur="if(this.value=='')this.value=this.defaultValue;"/>