I am using danish keyboard and XP plus lightwave 7.5.
Suddenly, while working, the keyboard shortcuts would stop working. For instance hide selected (-) would stop working and I just couldnt figure out why.
Well, today I found that it happened when I moved the object in the perspective view with Shift+Alt+Mouse move.
It turns out that by default Windows XP toggles between international keyboard layout and US keyboard layout when you press Shift + ALT!
Here is the solution:
Regional and language Options/Languages/Details/Key Settings/Change Key Sequence
windows is by default set up to switch keyboard language when you press left ALT + SHIFT.
Disable this and the problem goes away!
I hope this helps others, it certainly was annoying to me that shortcuts just stopped working :)