It sounds like your machine has a problem. What did the Seagate diagnostics say ?
Unfortunately Acer chose to sell many very different computers all starting out R3-131T. The last four is what designates whether a very capable or very limited machine. However with 8GB and a 500GB drive yours should be one of the better ones with a N3700 CPU.
That said just throwing parts at a problem without understanding what is the base issue is not very productive. I do know that the cable for the disk drive is delicate and you have to know how to open the clamp with a fingernail to remove the cable without damage.
What I would do is to remove the disk, mount as a slave in a desktop, back it up, then run a full set of diagnostics. If that came out good, I'd mount a known good drive in the R3 making sure all cables were good and connected properly then run another set of diagnostics on the machine.
Of course being retired and having several machines, I can take a day or two to get to the root of a problem. It is always the intermittants that are the most difficulot to find and usually takes A Lot of instrumentation to pinpoint it.
For Acer after three tries on the same thing, suggest you might ask for a replacement.