I am of the notion that suggesting sfc /scannow is akin to saying "I have no idea what the problem is or how to fix it".
sfc /scannow is designed to run one time when you install XP. The purpose is to populate the dllcache folder with backup copies of important XP files. Sure - you can run it manually if you want.
sfc /scannow does not replace missing or corrupt files in the system32 folder. It only cares about the dllcache folder. If you would like a little test case where you can prove it to yourself, I can post that (I composed it in hopes that the Microsoft engaged Support Engineer "experts" would stop suggesting it). Then you will know what sfc /scannow does and what it doesn't do.
Even when sfc /scannow runs successfully, you will only see a starting and complete message in the Event Viewer System log that looks like this:
Event Type: Information
Event Source: Windows File Protection
Event Category: None
Event ID: 64016
Windows File Protection file scan was started.
Event Type: Information
Event Source: Windows File Protection
Event Category: None
Event ID: 64017
Windows File Protection file scan completed successfully.
There is no information about what it did or what it didn't do.
Even if sfc /scannow finds something to do and replaces a file, you will not know about it, but you will have wasted your time and still have your original problem.
That makes suggesting it or trying it even more of a waste of time.