PowerEdge T610; all USB ports are not working

Dear Sirs,

with no apparent reason, all the USB ports on the server stopped working, despite the operating system (ESXi) recognizes the UHCI and EHCI controller regularly.

* at boot phase does not respond to any connected keyboard, it returns a Keyboard Failure and then start boot the operating system perfectly (ESXi) but it is not possible to access the BIOS;

* The DRAC does not detect a specific problem;

* all ports are regularly fed, by measuring with the tester output is 5V;

* all other machine functions seem not compromised.

Without USB all user interactions are compromised, as well as other related services (energy management, storage etc.).

I wish It would be possible, at least, to enter the BIOS in some way to extract further information. I look forward to a procedure.

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Thank you.