Upon boot-up, it says "error leading operating system".
I could insert a bootable USB with Windows 7 on it and attempt a repair.
I will try again.
The error about the missing operating system is a sign of (software) corruption of one or more "vital" sectors , that can happen on a perfectly working disk (hardware).
The error at 2% in TESTDISK analyzing the disk is INSTEAD a sign of actual corruption of one or more physical sectors (hardware).
While you can usually repair software issues by booting an alternate OS, you CANNOT repair a hardware issue.
Additionally attempting a software repair of a hardware error on a disk may make matter WORSE.
You have ONLY one option (short of consulting a data recovery specialist) attempt to salvage what data can be recovered from the disk (provided that the data is needed/worth something).
If you have a valid backup of the data (or the data has no value) you can of course play with that hard disk whichever way you see fit.
Take into consideration and keep in mind that I have the opporunity and am willing to buy and install an SSD to replace the HDD.
I can, in my spare time, attept to recover data from the HDD and transfer.
I just need to make sure that the SSD would fit and be compatible with this particular laptop (Acer Aspire 5250).
I don't see why *any* 2.5" SSD should not fit/be incompatible, it is a fairly common and recent machine with a SATA port, what is your doubt?