cannot try elemetary OS 0.3.2 64bit on my Thinkpad t420s

Question

I have created 3 bootable USB flash drives with

elementaryos-0.3.2-stable-amd64.20151209.iso  
sha-256 = ee737ffa6bf33b742c5a7cee17aa26dec5ee3b573cbbc4b53cbe2a2513c9197a

I used rufus-2.8 to create the flash drives.

laptop: thinkpad t420s

It boots up normally to the screen where you select the language and can "Try" or "Install".
When I click on try, it freezes and nothing happens.
(Install seems to work, I did 2-3 steps jus to check)

• I tried on 3 different keys and on 3 different usb ports (1, 2.0 & 3.0)
• latest Ubuntu 15.10 works well on 2 of the keys.
• I tried 2 keys on another computer and It worked normally too

Is there something I can look for in the bios?

Any ideas?

Answer 1

I managed to do it by forcing UEFI in the bios. This starts a different menu early where you I could choose "Try elementary os" and that worked fine.

The exact option in the bios is:

UEFI/Legacy Boot Priority :     [UEFI First]

(got other big grub problems after but that's another story)