Office XP problem

I have a couple of PCs on which the icons on the Office shortcut bar have been replaced by blank boxes. The tool tip will tell you what each box represents as it passes over each box. I’ve tried adjusting the settings and I have tried to restore the icons by uninstalling and re-installing Office, but the problem remains. The problem is a minor one but the users want it restored. I don’t know what else to try. Anybody have a solution?