how to enable NX support so to upgrade to windows 8

It should be available in that model.

Power down your Dell. When powering up your Dell, press F2 at the Dell logo and navigate to the security tab. The option should be available as shown:

hi, thank you very much for taking the time to try to help me here nice one mate. But its not how my BIOS is set up I have a dell studio 1555 and it is nothing like your diagram, that's what my issue is I cant find it in my BIOS setting any where I have been right through it and its so frustrating because I cant upgrade any further than where I am at now which is windows 7 Ultimate its ok don't get me wrong but I feel now what it cost me £800 when I bought this laptop and if I cant get this sorted out it maybe that I will have to now buy another one. But mate I got to say a big thanks to you for at least trying for me your good stuff mate all the best from Steve <ADMIN NOTE: Email id removed as per privacy policy>

I assume your BIOS looks like this then?

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/ensure-you-have-the-correct-sata-configuration-in-the-bios-setup-for-your-configuration/disable-usb-3-0-functionality/

If so can you tell me what your advanced and security settings are at.