Gandy, its not very wise advising an obvious novice to attempt to edit the Registry, apart from which, a clean re-install of Windows should not have resulted in a corrupted registry. The questioner has clearly not installed the graphics drivers and probably not the motherboard drivers either.
Shona, your PC should have been supplied with all the necessary disks containing all the drivers for it. If you do not have these, they can be downloaded from the websites of your motherboard and graphics card(if separate) manufacturers. To find out the make of these you need to look in the Device Manager. Right-click `My Computer' and from the pop-up menu select `properties'. This will bring up a tabbed box. Select the Hardware tab and then Device Manager.From the list provided, by right-clicking each item you can find the type of graphics card and any other item of hardware requiring drivers will have an exclamation mark on a yellow backgrond.When you have gleaned all the necessary information go to the various suppliers websites where you will find their drivers under the Support or Download sections.