No idea what you did, this works perfectly fine for me.
Code:
while(1)
{
	if(key_l)
	{
		mouse_event(MOUSEEVENTF_LEFTDOWN | MOUSEEVENTF_ABSOLUTE, 0, 0, 0, 0);
		wait(1);
		mouse_event(MOUSEEVENTF_LEFTUP | MOUSEEVENTF_ABSOLUTE, 0, 0, 0, 0);
	}
	
	wait(1);
}