I'm trying to install Kubuntu Saucy x86 on a rather old computer from an USB stick (USB legacy emulation enabled)
I also tried to boot Ubuntu Raring from DVD but getting the same problem:
The system boots into the setup menu (Something like this:)

        Kubuntu 13.10



        Start Kubuntu

   Check disk for issues

        Test memory

 Boot from first hard disk

When hitting Enter on Start Kubuntu, the Plymouth boot animation shows up, but when I hit Esc, I only see lots of something like these:

/init line 7: Can't open /dev/sr0: No medium found

After a minute or so I get into the initramfs shell with the notification that no medium containing a live file system was found.
As I said, this happens both from DVD and USB. I've used both media to install (K)ubuntu on other systems and didn't change anything on that stick.

The installed Windows XP boots without problems.

Please help me to get Kubuntu running on this computer.