Many laptops can experience the problem of having a very dim or almost black Laptop Screen. There are a couple of methods of detecting which part on your laptop is at fault. It will generally involve testing the laptop once a replacement part has been fitted. Most sellers will allow you to return the part within a couple of weeks if it is no longer needed but check before a purchase just in case.
If your HP Compaq Screen appears to be very dim with just a faint image of your desktop in the background then you could have a faulty inverter. This small circuit board attaches to the motherboard at one end and to the screen at the other. These can be purchased for around £20 and are very easy to replace. If this part does not resolve the problem than you may have an issue with the backlight within the laptop screen. This is a small thin tube, similar to the overhead office strip lights but on a smaller scale. This, when working correctly illuminates the panel. When faulty you may struggle to view an image. The laptop screen does cost a bit more than an inverter but it is necessary in order to get your laptop up and running again.