as you can imagine nvlddmkm.sys is part of the driver installation so simply deleting it will either cause errors or blue screens. there are a number of things that could be causing this to happen, such as corrupted files, a bad power supply, or even the card itself. the first thing i would advise is to do a clean installation of the display drivers, which requires you to use a piece of software such as Driver Sweeper to completely purge the associated driver files. once this is done, you can restart the computer and proceed to install the drivers normally.

if this fails, you may be looking at corruption in Vista itself or possibly with the motherboard chipset drivers. there's also a slim chance that you need to update DirectX software or frameworks for graphics-based software. if it comes down to having to test the actual hardware, there are limited options. the best way would be to test the card in another computer (preferably one with a different OS) and to test the power supply and RAM if you can. is there any reason in particular that the computer hasn't been used for a couple of years? there's always a possibility that your brother knew to replace something and never did