Hi, same problem here
Laptop : t520
Stick: Sandisk Extreme 16 GB
Disk is not visible in boot menu. I have tried USB drive from different vendor, all working. I have tried the disk with different laptop, all booted correctly. I have found many users with this problem(sandisk + thinkpad).
I have tried to complete repartion the drive using diskpart, main partition is FAT32 and active. The “Boot Disk” flag is set to “no”, but my other flash drive is also set to “no” and it is working just fine.
Is there a possiblity there is some hidden partition windows is not able to see ? I heard windows systems are sometime having a hard time working with multiple partitions on a flash drive
