When your laptop screen breaks, here's how to understand the problem, then fix or replace the laptop screen.

QUESTION The screen on my niece's XP laptop went blank and is now showing coloured vertical lines. When I plug in an external monitor the correct image is displayed onscreen. What can I do? denis93

HELPROOM ANSWER It sounds as though the laptop has developed a hardware fault with the graphics adaptor, the screen itself or the ribbon cable connecting the two together.

Since you're seeing a normal screen on an external monitor, the graphics card is the least likely culprit.

Assuming the laptop is out of warranty, your niece will need to cost up whether to replace the screen or find an inexpensive external monitor, I'm afraid. It's possible to buy a replacement laptop screen and fit it yourself, but these are often very expensive and such a repair can be uneconomical if the laptop is old. You can find replacement screens available for purchase on eBay. Prices vary considerably depending on the size and model of the screen but, as an example, 15.6in panels were selling for around £35-£65 at the time of writing.

You should be able to find a secondhand monitor available for less – perhaps for free if you ask around and look on Freecycle, or  similar service.

To diagnose your problem properly, you'll need to show the screen to a technician. For other readers suffering similar problems, please attach a photograph of the faulty display to your query so we can try to give you more specific information.

Laptoprepair101.com has a page collating various laptop screen faults along with a diagnosis. Browse through the examples and you may find a diagnosis for a fault that looks the same as yours. The site also offers tips on replacing the screen and checking to see whether you have a faulty connecting cable.

See all How to articles. Get free tech support in the Helproom Forum.

Visit Windows 7 Advisor for more Windows advice.