Alan,
  Sorry to hear about all the problems, have you done a chkdsk recently to
make sure that there are no problems with the hard drive?  I have never had
a file "disappear" after a defrag.  However data could get written to a bad
sector on the hard disk and be unable to read.  This could also affect the
install of programs if the files are being written to the bad sectors of a
hard disk as well.  Here are a few suggestions that might help.

A) Run CHKDSK to make sure the Hard disk is ok. (You don't want to waste a
lot of time troubleshooting software if a piece of hardware is having
issues.)

   1. Double-click *My Computer*, and then right-click the hard disk that
   you want to check.
   2. Click *Properties*, and then click *Tools*.
   3. Under *Error-checking*, click *Check Now*. A dialog box that shows the
   *Check disk options* is displayed,
   4. Use one of the following procedures:
      - To repair errors, locate bad sectors, and recover readable
      information, select the *Scan for and attempt recovery of bad
sectors*check box, and then click
      *Start*.
   *Note* If one or more of the files on the hard disk are open, you will
   receive the following message:
   The disk check could not be performed because the disk check utility
   needs exclusive access to some Windows files on the disk. These files can be
   accessed by restarting Windows. Do you want to schedule the disk check to
   occur the next time you restart the computer?
   Click *Yes* to schedule the disk check, and then restart your computer to
   start the disk check.

DIrections for finding the Results of chkdsk can be found by using this web
page.
http://janetalkstech.com/windows-tip-of-the-day-viewing-your-chkdsk-report

*Beware if it says if found any bad sectors on the drive.*

B)Verify that IE can be brought back to working conditioning by performing a
reset.

   1.

   Close any Internet Explorer or Windows Explorer windows that are
   currently open.
   2.

   Open Internet Explorer by clicking the Start button [image: Picture of
   the Start button], and then clicking Internet Explorer.
   3.

   Click the Tools button, and then click Internet Options.
   4.

   Click the Advanced tab, and then click Reset.
   5.

   In the Reset Internet Explorer Settings dialog box, click Reset.
   6.

   When Internet Explorer finishes applying default settings, click Close,
   click OK, and then click OK again.
   7.

   Close Internet Explorer.

   Your changes will take effect the next time you open Internet Explorer.

C) If the above two things have got the system going again, try the install
of Firefox again with the latest installer.
http://www.mozilla.com/en-US/firefox/

Sorry if it seems a little long and winding, but hopefully this will point
you in the right direction.  If there are no bad sectors and the system
still is not cooperating, then a repair might be advised.

good luck,
Derek

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