I actually am starting with Sony Vaio box that runs slowly...
I figure I will replace the motherboard first, but that is just a
quess...
SkyHigh's suggestion is good -- problem w/ brandnames, some, is they
can be a Chinese jigsaw to figure. I'd add a qualifier to that -- get
a *generic* ATX case that will fit virtually all standard sized
motherboard mounting holes, with the same holding true for power
supplies. What's left -- a hard and optical drive, and things start
to look pretty simple from the assembly point. Meaning, there's more
time to concentrate on the component factor, researching and
understanding what's going inside a box, facilitating "swapping",
instead of unwanted proprietary part hairball issues. Also, since the
box is square one -- think about one with adequate cooling. Starting
up a "clean machine" shouldn't involve heat, or be fundamentally
problematic about causing software-related glitches and potential
hardware failures.
I've got a lot of older gear I built that's been holding up "OK" over
the years. Not worth much now if I were to sell the stuff -- which I
guess means cheap *and* good. Good being a matter of focus and
application, and what-if scenarios when eventually, as will happen,
stuff quits, breaks, or gets too outdated and has to be replaced.