What is the simplest way to reset PC to default settings?
If you are talking about the physical PC, removing the battery
from the motherboard (and then replacing it) will result in all the
on board RAM setting being set back to default. However in the BIOS
of most PC systems there should be a setting to restore the
"factory defaults" or "Factory settings".
Operating systems are more difficult to reset, for example in
Windows you can "roll back" to previous backed up settings (if this
feature has been enabled).
Note: Resenting the board defaults causes the on board clock to
loose time, and can also result in some installed programs not
running properly.