If you click on "my computer" do you see the sd card displayed, try clicking on it if its visible and see if opens properly, if it does it means "autoplay" disabled, also when sd card is inserted usually windows will chime when new hardware is found but sometimes these sound alerts can disappear to due to minor problems with windows files. Also the "usb icon with green tick" for safely removing usb and other storage hardware can disappear from the toolbar area confusing the situation more.
However if sd card reader is working correctly it should appear in "my computer" and device manager. If you have checked "my computer" and certain the sd is not appearing then navigate to device manager and see if any yellow exclamation marks appear and verify that the sd card reader drivers are installed, its possible during the repair of the laptop they neglected to install the driver. In this situation if the driver is not installed go to manufacturer's website for the latest drivers.