Big problem has arisen. My machine has started continually 'rattling its cage' i.e. it is incessantly, noisily, unnecessarily and lengthily checking all the removable bays (A, E and F) whenever I start anything up.

The problem arises not only with M$ but with third-party software too. In recycle bin, for instance, it won't proceed to delete anything until it's finished checking and then tells me that A, E and F cannot be accessed. (They couldn't, because the bays are empty.)

I have run diagnostics and AVG, ZoneAlarms, etcetera and the problem is not there because of any new software or because of viruses or such things. It is because I have somehow inadvertently and unknowingly altered some settings or other.

I believe the knub of the problem is msDOS. In System Properties (aka device manager) it tells me that the removable drives are in 'MsDOS compatibility mode' but doesn't tell me how to exit that mode. (Isn't that just the way with most 'help' files - vague, obtuse, simplistic or unintelligible to the ordinary user, take your pick - just a waste of space!)

Any help to this non-techny would the appreciated!  

   If my memory serves me correctly, MSDOS Compatibility Mode is something you want on those drives and is not causing your problem.  MSDOS Compatibility Mode has to do with how the partition on the drive was created.  The only way to get it off is to repartition and reformat that drive without it.  
   My guess is that somehow those drives were put into the Path.  Installing a game or DOS software may have done that.  To see what the Path is and to edit it, right click on My Computer. Go to Properties: Advanced tab. Click on the Environment Varialbles button (at the bottom).  In User Variables for Your Name or System Variables, make sure that those drives are not in the PATH variable.  If they are, edit it to remove them.
   Hopefully, that will solve your problem.  If not, let us know here and maybe someone can figure it out.

Don't use games, don't use partitioning!   In fact I only use DOS to get out of scrapes when the machine is misbehaving and to use scanreg /fix and /opt and unWindows scandisk sometimes!

But the environmental variables aspect is a fresh approach I need to look into, thanks. As far as I can remember from my last visit there the EV tab lists about four entries - when I go back there would it be safe to delete every entry to see what happens when I reboot? Or would this here old non-techny be courting even greater disaster?

postpostscriptum - Yes, I've now looked at EVs and they read

Quoted Text PATH C:\WINDOWS;C:\WINDOWS\COMMAND;C:\;C:\WINDOWS\SYSTEM;C:\PROGRA~1\COMMON~1\ROXIOS~1\DLLSHA~1;C:\PERL\SITE\BIN;C:\PERL\BIN PROMPT $p$g (what does this mean?) TEMP C:\WINDOWS\TEMP TMP C:\WINDOWS\TEMP Note PATH TEMP and TMP are the same as in autoexec.bat

These are no different from what they have always been so doesn't seem that EVs are the culprits

(postscriptum afterthought - what is a 'minimum member'?)

   I guess my memory did not serve me correctly.  I was on vacation at the time when I wrote that and I did not want to go look it up.  
   Here is a link that may help you concerning that - http://home.earthlink.net/~leetutor/FixWin/Hardware/msdos.htm