here's the situation. I've got on a USB stick lots of files of different formats that open quite naturally when I double-click on them, EXCEPT files to do with the Net (HTML, CSS, PHP). i copied them to my desktop, where I can now open them with a preferred app. so why can I open a .doc file on my stick, but not a .css one? It seems I haven't got the necessary permissions needed to alter group permissions which are set to none (although other files like text files have the same set of permissions but i can still open them). I also checked the default.list and mime.types files ( as per suggested in another thread) and every thing is apprently as it should be; so I am puzzled. Can anybody help me find how to open those files while they're still on the stick?

type sudo nautilus ---> enter password now try it. right click the file and open with your choice

Indeed, the command works as a new nautilus window opens. However, as soon as it is closed, then another nautilus window opened, the files don't open any more. So that means that I have to go again through the process you suggested and i rather wanted not to have to do it again. Is there a configuration file that could be altered?
By the way, the following is the error message that I get when running "sudo nautilus":
could that give a clue as to what i have to change?
Thanks in advance for your replies,

Obviously if you can read the files while root, but cannot read the files while not root, the problem is file permissions. The solution is to change the file permissions.

right click the file click properties click permissions and change it to your user.

that's exactly what I did before I posted the thread. All the files on my stick and their copies on my desktop are owned by me, yet only the latter open when i double-click on them. The stick files do open if you right-click on them and do NOT choose the default application. you will agree that this not very convenient, especially with frequently-used files. I am not an experienced linux user, by far, but suspect that I need to change settings somewhere so as to alter permissions.
There are 2 more things i have noticed (are they clues?)
-I can't change any permissions of my stick files (group, others, execute files) and if i want to change the name of the group, I am told that I can't because I haven't got the necessary permissions
-The permissions of the stick do not appear (could not be determined)
Also, I had a go at using chmod to see to what extent i could alter file permissions but don't seem to have got anywhere. However, i've got to point out once again that I wouldn'trust myself in any way regarding performing any task whatsoever. So all manners of comments, suggestions are welcome. (And remember that .doc, .odt and other commonly used files open with no problem)

only time I have seen this is when the files were using encryption. this has happened many times.
Last resort down load puppy linux boot it up it runs in ram it is 96 mb a complete gui.
now open the usb drive then open your drive sda1 drive drag the files to sda1 this will ask you to move them or copy . copy them . now open them. If this does not work. You will have to go to that usb drives home website and read about there encrypted device. you may have to use M$ to access it.
Good luck.