Tricks useful on Dell computers (at least on a Dell Inspiron 4000):

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Type ctrl-alt-d during initial booting to start hard drive diagnostics.

I had been suspicious that my disk was beginning to fail (the computer had
been acting progressively stranger over the course of a couple of weeks,
and near the end Linux found a number of unrecoverable bad blocks that lead
to files being sent to lost+found).  ctrl-alt-d confirmed the problem by
showing 27 errors on my disk, so DELL sent me a new disk.

One web page said that ctrl-alt-d is called the 90-90 test, as it catches
90% of disk problems in 90 seconds.

(Setting the BIOS option to do full power-on-self-test (POST), might do the
same tests?)

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The standard procedure for installing a new bios won't install an older
version.  To do a "force flash" of an older version of the bios, do the
following:

(1) insert the floppy that is normally used to install an old version of the
    bios, and reboot the computer.

(2) It will claim to have installed the new version, but hasn't (which you
    can verify by going into the BIOS and looking at the version number).
    Type "dir" to see the list of files on the floppy.  One of the them is
    bios installer, like "bios-name.exe".  Run this installer with the
    following option:

    bios-name /forcetype

and follow the instructions (this is what Dell support told me on the
phone).

Some random web pages also mention trying "bios-name /forceit /forcetype".
Another unknown option is "/jabil".