How was the projector connected to the laptop, were you using HDMI or VGA cable? While the laptop is connected to the projector press the Windows key + P at the same time and select between Duplicate or Extended display then press Enter. If these will not work try to uninstall/reinstall the graphics card driver from Device Manager.
- Go to Device Manager and uninstall the graphics card driver.
- Open Programs and Features and uninstall anything related to the graphics driver.
- Download and install the latest driver from the manufacturers site.
- Once installed reboot the laptop for all the changes to take effect.
- Do test it again after the reboot, press the Windows key + P at the same time again.