It seems like you are not actually switching to any new window. You are supposed get the window handle of your original window, save that, then get the window handle of the new window and switch to that. Once you are done with the new window you need to close it, then switch back to the original window handle. See my sample below:
i.e.
String parentHandle = driver.getWindowHandle(); // get the current window handle
driver.findElement(By.xpath("//*[@id='someXpath']")).click(); // click some link that opens a new window
for (String winHandle : driver.getWindowHandles()) {
driver.switchTo().window(winHandle); // switch focus of WebDriver to the next found window handle (that's your newly opened window)
}
//code to do something on new window
driver.close(); // close newly opened window when done with it
driver.switchTo().window(parentHandle); // switch back to the original window