Maybe your chips are getting fried:(
It might be time to invest in a new (and better) machine.
If this is your main hobby.....then I would seriously suggest that a good investment in a very decent machine that will see you through the next few years including TESVI, would actually be worth the pain of the repayments.
If the parental bank is uncooperative then talk about other ways to fund it.
Normally I'd advise always saving up first....dont get into credit debt.....you'll get enough of that later with having to borrow to fund a car and a mortgage around your neck. But Im saying here....this is your special hobby.....so it might be worth it.....most people get phones costing hundreds on monthly contracts.....so on that basis spreading a really good PC (great PC) over a couple of years would seem sensible to me.
Personally....I would be loath to buy second hand. It all comes down to personal circumstances.