robes1986-- Apologies if I am wrong, but by the username, I would suspect that you are studying for the legal profession. If I am correct, would it not be practical to consult with one of the college tutors about the problems that you have experienced. I am sure, they would offer better advice than perhaps Consumer Direct click here could offer.
Having said that, the time span from August 2004, doe's seem to imply that you have had 'reasonable' use of the product. But this doesn't say that things are correct in your views, and those of Evesham's. I have always found that Evesham do offer that little bit more than perhaps other companies, in respect of customer care, if forum's like this are anything to go by.But I know those views are perhaps not solving your own problem at present.
My only suggestion at this stage, is for you to make it quite clear that you are requesting further help in getting a full and capable working machine. If necessary, seek advice on the six year ruling of consumer law,either by consulting Consumer Direct or someone with legal knowledge of consumer law, if any warranty claims are being refused.You do not seem to mention the type of warranty being provided on this product, and knowing more about this could make a slight difference perhaps.
Regarding losing work, then the golden rule is to always 'back-up' everything that you do, but I suspect that you already know and do this!.
Your problem is a slight 'blip' in the system, nothing dramatic as you would seem to imply. Much worse things have happened to other people, due to sales and service confusions. Think, what is your gain is Evesham's loss in respect of a possible sale.
Taking about Dab's excellent service is neither there or here, until you use the service. Building your own computer may prove totally successful, then on the other hand, what happens if compatibility of parts comes into the equation. I am sure Dab's will not send out a service engineer to solve the problem. Emails, telephone calls will be the order of the day, to seek remedies of any problems. I would point out that Dab's have had fair criticism in the past for poor service, and they have also had congratulations on good service, that is the workings of the business world. Whether this will get better or worse, now that Dabs is a BT owned company, time will only tell.
I would perhaps suggest that you start your own thread, and let the forum know how you get on with your self build!.