The definition of an 'inherent fault' is an important one here. It refers to a fault which was present at the time of purchase (such as poor quality components or the use of poor manufacturing standards). With most items there's normally an automatic legal assumption that any problem occurring during the first 6 months must be due to an inherent fault. (Thereafter it's up to the purchaser to show that an inherent fault is the most likely cause of the problem). However the fault with your laptop's software is unlikely to have been present at the time of purchase. (It's far more likely to have arisen because you've installed conflicting software, downloaded a virus or allowed malware to find it's way onto your hard drive). A court might well rule that the normal '6 month rule' does not apply in your case.
It's pointless challenging Dell about their decision. You could try arguing your case with Curry's, but you'll almost certainly have a major battle ahead of you. In practice it might be simplest to post again, in AB's 'Technical' section', telling us which version of Windows you're using and which disks were supplied with the laptop. (For example, did you get a full Windows disk or just a 'recovery' disk?). With a bit of luck you'll get the same information that Dell wanted to charge for, completely free.
Chris