If you are using SnowFlat theme than do following
In qa-theme/SnowFlat folder find and open qa-theme.php file
Around line #282 find below code
public function sidepanel()
{
// remove sidebar for user profile pages
if ($this->template == 'user')
return;
$this->output('<div id="qam-sidepanel-toggle"><i class="icon-left-open-big"></i></div>');
$this->output('<div class="qa-sidepanel" id="qam-sidepanel-mobile">');
$this->qam_search();
$this->widgets('side', 'top');
$this->sidebar();
$this->widgets('side', 'high');
$this->nav('cat', 1);
$this->widgets('side', 'low');
if (isset($this->content['sidepanel']))
$this->output_raw($this->content['sidepanel']);
$this->feed();
$this->widgets('side', 'bottom');
$this->output('</div>', '');
}
Remove or comment $this->qam_search(); within the function. So finally you will get code as below
public function sidepanel()
{
// remove sidebar for user profile pages
if ($this->template == 'user')
return;
$this->output('<div id="qam-sidepanel-toggle"><i class="icon-left-open-big"></i></div>');
$this->output('<div class="qa-sidepanel" id="qam-sidepanel-mobile">');
/*$this->qam_search(); disabled search*/
$this->widgets('side', 'top');
$this->sidebar();
$this->widgets('side', 'high');
$this->nav('cat', 1);
$this->widgets('side', 'low');
if (isset($this->content['sidepanel']))
$this->output_raw($this->content['sidepanel']);
$this->feed();
$this->widgets('side', 'bottom');
$this->output('</div>', '');
}