PartitionExpert booting from CD on DELL GX 520

HI,
I had some trouble to create a new partition on my HD using Partition Expert 2003.
(The message after rebooting was "Disc not found")

So I've created a bootable Acronis Partion Expert CD to start the software from CD (I read the hint in this forum)
But unfortunately after booting from CD my keyboard and mouse will not be recognized and I cannot make any input. Mouse and keyboard are connected via USB and run without problems under Win XP SP2.
My maschine is a Dell GX 520. What can I do?

thanks