Someone may come along with better advice, but here's mine..

Consider eliminating all your guest and limited user accounts, then adding them back one at a time. Restart after you've added each account, then see if everything works properly before adding another.

That worked for me when I ran into file sharing roadblocks as I bumbled through setting up a home network.

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@gomom wrote:

won't I lose all the files that are in them?

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I'm pretty sure you won't lose any user files, but be safe and transfer them to the 'shared document' folder before you make any changes. It's in My Computer.

Okay, I did as you suggested. There weren't too many files worth saving in those accounts, so I just saved them to a disk from the admin account. I deleted all the limited user accounts, restarted the computer, and then created a new limited user account and... the same thing happens. I am still getting the shell failure. I just dont understand what could be causing this. I've looked all through the dell forum, and a google search or two took me to some similar  sounding situations, but I haven't found any solutions that have worked. My windows updates are all current, I am running the Mcafee package that comes with Dells, and am free of viruses (signatures are also up to date). Why would this only happen on the limited users? As I said the admin account works fine- the others are my kids' , and I don't want them to have administrator accounts, but they save homework papers etc. and need to be able to get to them. Thank you for trying to help- if you or anyone else has any suggestions I am all ears!   

This doesn't really sound like its usual effects, but have you scanned for spyware? Try Adaware or Spybot-Search and Destroy. You can also get a reliable second opinion about your virus status by using the online scan at the Panda Software site.

My guess is that your problem is being caused by corrupt files in XP.

I would first try XP's system restore. If that fails, see if you can repair XP from the installation disk. You may also have a Dell disk that restores everything to its original factory configuration.

The ultimate repair is to reformat the hard drive and reinstall XP. Reformatting isn't particularly difficult or complicated, but save it for last. It will erase everything from the hard drive, which means you'll have to reinstall all your programs and settings.

We have now reached the very bottom of my well of knowledge..:)

Well I think I have finally solved the problem. Adaware found more stuff, but didn't get it all, so I installed Spybot S & D and Spyware Blaster. That finally seemed to do it. It seems I had some residuals from Myway bar that were calling themselves other names: Ibis, search bar ,etc.,etc. I think it was Spyware Blaster that finally did it- after removing everything the others could find, it stopped whatever they couldn't find or remove from running. I don't know exactly what that thing (myway or it's aliases) does, or how it kept coming back(it had been uninstalled before), or how I got it in the first place for that matter, but whatever it was seems to have been reponsible for the shell crashing repeatedly.       So thank you again Hgunn for your input- I appreciate your taking the time to resond- And maybe this will be of use to anyone with a similar problem. I'm keeping my fingers crossed that it stays fixed

Sounds good and you're certainly welcome. I update, then scan every week with both Spybot and Adaware. It isn't unusual for one to find something the other missed.

To bring this episode to an end, deactivate System Restore, get rid of all it's current files, then restart your computer and reactivate it. This starts it with a clean folder. Your present restore files are almost certainly infected with the same spyware that's given you all this grief. Your spyware tools can't clean them, so they're waiting to get you again.

Thanks ! I will do that.