Powerpoint is freezing in XP

All the presentations in Powerpoint are freezing when I try to add a new slide. The cpu use is growing up to 100% and stay at this stage until I kill the apps. I tried the same presentations on differents machines: every time the problem occurs withWindows XP and Office XP. Never on win2000 with Office 2000. I tried with files made on Win2000 or on a XP machine: same pb. What can I do?
Thanks for yours answers