In answer to your question: yes, by all means, write up a formal complaint. HOWEVER... get someone familiar with English to do it; your letter above hurts my head and from their perspective, will make you come off like a whiny kid rather than a dissatisfied customer.
John is correct, you want to include as much concrete detail as possible: names of the clerks, dated sales receipts, dates and times of support calls, etc. (basically lay out a specific timeline of everything that happened and how much time you've invested in dealing with the problems).
I'd suggest sending copies of the letter to the managers of both Sony Style stores as well - make note of your displeasure that they're selling refurbished laptops as "new", since as you note, you did specifically start into this with the idea that you were buying a NEW laptop. It would be one thing if this happened at a Best Buy or something, but that it's happening at Sony's own branded stores is especially ridiculous.
When you say you returned the second scratched laptop and they "helped you set up a new Windows", do you mean they actually helped you reinstall Windows fresh on that scratched, obviously USED laptop?? I wouldn't accept that for five seconds - this whole escapade started off with them selling you (or your dad) what was supposed to be a NEW laptop; I wouldn't rest until I was actually in possession of a NEW laptop of the model you THOUGHT you were getting, or the closest BETTER equivalent. Not saying that they should give you something substantially better, but what you end up with certainly shouldn't be a LESSER model than you THOUGHT you were paying for.
They may argue that since you were paying less, you should get less, but that's bullshit: you were paying a sale price for what they claimed was a NEW unit of a certain model, and you should end up a NEW unit of AT LEAST that model. Period.
Finally, check out
www.consumerist.com - they have a lot of really good tips for registering complaints with companies, including a list of the types of people to send your letter to, how to get those people's contact info, and how to word and structure your letter.