virtualbox.org

Oracle VM Version 5.1.6 r110634 (Qt5.5.1)
PC Sony Vaio Win 8.1 64bit

I would like to create in a PC(1) running with Win 8.1 64-bit, a VBox Win8.1 64-bit, but the creation presents a list of only 32-bit systems.
The strange thing is that the same version of Oracle VM, in another my PC(2), very similar to the first, like features and software, shows a list that includes also the 64-bit. On that PC(2) I could install two VBox Win8.1 64-bit (one converted later without problems in Win 10).
I compared with CPU-Z, the two PC finding no relevant difference, in particulre In both defined Vt-x (enclose report 1). In Windows functionalities no Hyper-V found in both PC.

What other controls or changes should I do?

FAQ: I have a 64bit host, but can't install 64bit guests.

CPU-z only tells you that VT-x is available, not that VT-x is enabled in the BIOS and not used by something like Hyper-v.

Ok, solved.
Your observation suggested to me the solution. Thank you
I enabled Vt-x in Bios. Now VB Win 64 bit are possible.
I get mysterious why was set by the manufacturer to disabled.

Thanks for reporting back.

Thanx for FAQ.
I have Windows 10 64bit. I enabled Hyper-V and my guest 64bit op.systems doesn't work nor can't choose a 64bit type.
Now I disabled Hyper-V and working again.