Found a problem. Faulty CPU. After replacing no issues at all. Windows and Ubuntu running without any problem.
Hi   I got my hands on Optiplex 5260 AIO. Original drive was dead. No way to recover anything. A had an extra 320GB HDD for testing and that is not a problem. Problem that I can't install anything.  Tried Ubuntu 20.04, 18.04, 16.04. Installation always  always hang at the same moment.   Tried windows 10. Download from Microsoft with original tool. USB installation. After loading windows logo pc always reboots.  Latest 1.12 bios. Any suggestion what to do next will be appreciated.  Thaks
Optiplex 5260 AIO can't install anything