Windows Look and Feel - wrong display

I have written a program with UI that I can switch to Windows L&F. It
worked ok and still does on all Computers I run it on, except one. On
this one PC, text fields are not displayed "three-dimensionally", but
completely flat, the font colour of disabled buttons does not become
grey and I don't know what else. I tried to run the program in
different JREs, 1.4.02, 1.6.0_01, 1.6.0_05, the same results.
Operating system is XP, but on other XP PCs it runs correctly (and
also on this one some time ago).
Can anyone tell me by what the behaviour of the rendering in Windows
Look & Feel is determined, what could explain that the behaviour on
this PC has changed?!

Thanks,
Winfried