[iTunes] Corruption of iTunes Library? Vs. problem with iPod itself?

[Carol F. Bruml]

Quick question: What does the exclamation point that appears after some, but
not all, of the tune numbers in my iTunes Library mean? Does it indicate
that the album artwork has been downloaded, or does it indicate something
else, altogether?

And then, the complicated question(s): I am now having problems with a
second iPod (80 Gig iPod Video), which says it has synched, but which is
missing somewhere near half the tunes in each playlist that I have checked,
so far. Why would this happen?

It has been suggested that there is corruption in my iTunes Library database
- or a problem with the iPod itself. The software and preferences are
brand-freshly installed. If there is corruption in the Library itself, how
does one find and repair that sort of problem (which I have never heard of
before)?

Should I just try creating new playlists, on the assumption that perhaps the
lists are in some way damaged? Can I do that by dragging the contents from
one of the present ones to a new list, or do I have to start over by
dragging the contents from the main Library file, which would be MUCH more
time-consuming?

This new/refurbished iPod also had problems with synching in the first
place, and kept stopping, balking during the sync process, and telling me
that its hard drive could not be read from or written to. Hmmm...two similar
messages on different machines, makes me wonder about the Library. However,
this one is still returnable. Should I keep trying, or return it?

Note: all of the problems with both iPods occurred right after I upgraded
iTunes to version 7.6. I don't know any easy way to go backward to an
earlier version; if you try to revert to an earlier version of iTunes, you
get the message that the Library cannot be opened because it was created by
an earlier version of the software. I do, presumably, have either one or two
recent, earlier versions on my backup drives.

I also have the entire iTunes Library, backed up about a month ago, before
all this happened.

Please advise.

Carol