<<I thought keeping my system free of unused software and regular fragmentation was all that I needed to keep things tidy as far as XP starting and loading all the pieces it needs. Is there another factor?>>
Windows is just the operating system...the system is primarily composed of various electronic components which may be at the root of any users poorly diagnosed problems...bad hard drives are routine for creating scenarios where the owner/user doesn't even think that it's a hardware situation at the root of her/his problems.
Failing hard drives may result in files being unable to be read properly...damaged files...disappearing files/partitions...and other effects which may come across to the unknowing user as something other than a failing/bad hard drive.
A clean install of the O/S...after running the appropriate hard drive diagnostic with no problems...is, IMO, the sensible way to overcome the problems which may be caused by a failing hard drive.
The rest of the system may be perfectly functional...but a hard drive is the base upon which the partion is created and Windows is installed.
For me, it makes sense to verify the functionality of the hard drive before throwing money away. A hard drive costs a lot less than a total system with a new version of Windows.
As for maintenance on a system...all I can say is that it isn't as simple as you seem to think it is. Files become damaged all the time...and the system or programs on the system may malperform because they are damaged. There's always a potential for heat issues caused by improper cleaning/ventilation or lack of owner/user care in that area.
IMO, there's no simple answer to your question...a computer is a sophisticated instrument that we all would like to pretent is as simple to use/maintain as our TVs are. We just turn those on and we have the goal.
The basic complexity of any computer system or situation...is one reason why you will see so many varying comments at a forum like this...on what a user may think...is a simple issue.
Edited by hamluis, 10 April 2012 - 05:19 PM.