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meghane-e - do you have a device attached? If so what happens when you unattach/eject the device? As
theducks posted, different toolbar setups are used when you have and don't have a device attached.
Do any of the icons show in the toolbars, e.g. Preferences and Edit Book? Or is it just the optional plugins?
Is there is a chevron ('>>') at the right-hand end of the toolbar, if so, click it and the missing icons will probably appear.
Added: I suggest you backup your configuration folder, see
How do I backup calibre?. It unlikely to be very big, zipped up mine is about 15KB.
Make sure you know how to restore it, and try doing so. I've come across situations where backups exist, but the owner hasn't a clue as to what to do with them when they need to do restore; and I'm not only referring to individuals, some pretty big businesses too.
BR