Flash Drive and Boot Reset or Computer Death

I have a custom Flash Drive. It works great in 90% of computers, but in the
other 10% it has two problems: 1) it randomly resets the computer (no blue
screen!), and 2) will not allow a boot (stuck on the PC logo before the drive
boots).

This flash drive mounts as a Hard Drive. It has a read-only partition table
and boot sector.

If anyone has any ideas or good references, please let me know.

Thanks,
-Erik