Thanks for the help! Some interesting reading there!
Unfortunately, the SafeBoot "registry fix" (for XP SP3) didn't seem to work. XP still boots back to Normal mode after changing settings under msconfig!??
I have also "repaired" Windows XP installation via its installation CD/DVD, but again there was no improvement, computer still boots back to Normal Mode.
I'm currently scanning the system with some other anti-malware/anti-spyware programs, but so far nothing of concern has been found.
A couple of extra notes, though.
Quite often when shutting down, a message box appears that "explorer.exe" is still trying to shut down and it has the option that I could end the program now. The system usually doesn't shut down then ("hangs") until I select to end explorer now. This usually occurs after I've browsed the system via Windows explorer, and then closed Windows explorer. But this message box often appears and causes a system hang-up.
Also, when changing desktop video resolution, the resolution doesn't seem to take/change immediately!? I might have to change to another resolution setting (which may or may not take), and change (back) to the resolution setting that I want!?
It seems the system may be a bit laggy, it doesn't always respond to changes immediately.