Thank you yancek and jefro for answering.
The Ubuntu disk has been plugged (directly to main board with sata cable) as test.
My main goal is to plug disks from NASes, but since any of the NASes disk was allowing windows 7 to boot, I did a quick counter proof plugging my ubuntu pc's hard drive.
The BIOS drives boot order is correct, as matter of facts is windows 7 booting and because it hangs, when I reboot it it goes to prompt for
"Repair windows installation"
"Boot windows normally"
Definitely it is the windows 7 disk that boots the pc. So I un-plug the "linux" drive and I run a clean boot.
As soon I re-plug ANY linux partitioned drive, windows 7 boot hangs at the early first stage.
After a Clean boot and shutdown, I plug any linux drive - progress bar repeats some progresses and last blank screen with a cursor (no BSOD no messages: hanged)
After the hang, I Ctrl-Alt-Del - the prompt with two option (which obviously none of them works)
What I can say is that either on NAS disks and on my linux drive there are both ext3 and XFS partitions (but I think this makes not much difference)
Do any of you have a windows 7 64 bit installed where to plug a linux drive
This would be an interesting comparison... Windows 7 Enterprise 64 bits I'm using is a 90 days evaluation downloaded original from MS website.
While the mainboard is a recent Asus P8P67 Deluxe rev. 3.0 which I also updated the BIOS trying to fix this issue.
Thank you for any tip or test