Extremely poor customer service

In October 2014 I spent £800 of a Hewlett Packard laptop for my son and in April it stopped working. I took it back to PC World at Elk Mill in Oldham and a member of staff tested it and diagnosed a hard drive problem and scanned the bar code inside the battery compartment to ensure it was still within warranty. They sent it away for repair but the engineers returned it saying there was physical damage to the casing that wasn't covered by the warranty so they wouldn't repair it. The staff member read an engineer's report from their screen which talked about an 'alignment problem', saying that because the computer was dropped, the hard drive was out of alignment and therefore wouldn't work, and that the warranty wouldn't cover it.
As far as I am aware, the computer has never been dropped. I asked if they computer could have been damaged in transit and they were adamant it hadn't been although when I asked for proof they couldn't provide any. When I asked how much it would cost to be repaired they said there was a basic £50 charge and "the cost of parts". I asked how much a new hard drive would cost and they wouldn't tell me. When I asked if they thought it strange that a retail unit wouldn't tell me the cost of a product, they (two staff members by this time, after I asked to see a manager)said "all hard drives are different, we can't tell you the cost." When I asked if they sold them out on their shelves (as my local computer store in Middleton does, £52 for a 1 terrabyte hard drive) they just stared at me blankly and said again that they couldn't tell me the cost. When I asked what 'out of alignment actually' meant one of the staff said "Well, alignment is a word..." and I asked her to stop patronising me, she then told me to stop raising my voice, which I wasn't doing (I'm sure they'll have it all on CCTV.) Both members of staff treated me like something they had stood in, one of them said: "right, I am just walking away now" and I felt insulted, demeaned and patronised. I've spent £800 and PC World couldn't give a mokeys. When I asked to be shown the damage the engineers were talking about, they said they couldn't show me. I then had to wait 10 minutes while some poor, low resolution black and white pictures were faxed over.
The engineers report said there was physical damage to the unit, I asked what was meant by 'the unit' - did it mean the laptop as a whole or the hard drive specifically. I was told 'the unit'. When I asked if the engineers had actually tested the hard drive, they said yes, but couldn't produce what I considered to be evidence that they had even got that far.
As a customer I was expected to accept, without objection, what the engineers said and accept my £800 had gone for a burton. I don't.
I am expected just to walk away and accept the damage to the casing in the computer is my fault. I don't.
It seems that I am expected to be patronised and insulted by shop staff, merely for raising an issue. I don't.
It seems that I should treat the fact that PC World refuses to divulge to cost of a new hard drive as standard customer service practice. I don't.
Just five minutes surfing the net established for me the lousy reputation that PC World has when it comes to dealing with customer complaints. They refused to tell me how much the damage to my computer would cost to repair, I would suggest the damage to their reputation is far more expensive. Never will I visit or buy anything from them again, and will advise my wide circle of friends and relatives to steer well clear. PC World, your attitude stinks.
Finally, I asked the staff if they get a lot of annoyed customers like me, and she said yes. I asked he if she thought that told her something. She looked me straight in the eye and said no.
Oh well, on to trading standards. I work for a council so a quick chat with a colleague should point me in the right direction.