I found the solution!
the problem:
Windows 8 OnScreen keyboard quit displaying on logon screen
The solution:
Link Removed
or
CMD in administrator mode
bcdedit -set TESTSIGNING OFF
For your information, i had the problem with a Customer tablet: Samsung X700t ( with the 3g module).
After the install of Windows 8, when it reboot on the screen for select the color and the machin name, NO TACTIL!!
i install 4 times:
1) Windows 8
2) Windows 8 Pro
3 Windows 8 PRO FR
4) Update from Windows 7 with the tablet ful fonctional
and at last, trying the :bcdedit -set TESTSIGNING OFF
All was working fine.
Thanks for your support.