Well, I fixed my friend's mom's Win7 64-bit HDD PC. Over the phone, over a span of nearly three hours. Whew.
Thankfully, my friend didn't give me any guff, and dutifully executed my commands.
Symptoms were, system stopped responding, wouldn't shutdown properly.
Turned out, it was because BOTH Norton AV/Deluxe AND McAfee Scanner were installed.
Had the unfortunate experience of having worked on a rig that had two A/V softwares installed on Win7, and the symptoms were that the I/O performance of the HDD drops to nearly zero.
Checked temps, wasn't throttling on CPU or GPU.
Checked SMART, no pending sectors / re-allocated sectors, looked good.
Checked for mining trojans with Malwarebytes. None found.
Was given a clue, when Norton popped up a warning, after McAfee popped up earlier while fixing / diagnosing things.
Whoops, two A/V suites installed, NOT GOOD.
Once the Norton Removal Tool finished, it rebooted OK again. And with McAfee removed, things were flying along.
I put MS Security Essentials on. Lightweight, and works.
Updated Win7 and IE. Left my friend running a HDD surface scan with HDTune.