Hi I took a new USB stick and that was half of the trick. The other problem was that my ASUS mainboard (M4A89TD PRO) had an option to use only 3 of the 6 cores, but with higher clock then.
Deactivating that option ("Core Unlocker feature") in the BIOS lets start all images without problems (I tried Yakkety Yak 64bit, Ubuntu 16.04 64bit and Kubuntu 16.04 64 bit). Lucky me the boot problems lead to a full BIOS reset, so that I recognized the result of this option. Thanks for your comments. regards, Marcus P.S: Issue solved in my eyes -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1588539 Title: boot from USB stick doesn't work To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1588539/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs