Honestly, I never really bothered much with the persistence thing, but I did
put it there with Unetbootin on the Linux Mint sticks I made, and I don't
recall any success there (though I wasn't unable to boot like you; that must
be a problem with your BIOS or hardware, because a USB stick was how I
installed Trisquel 6 on the laptop I'm using right now).
Why don't you just create a small partition on your hard drive for testing
Trisquel? That's what I would do personally, rather than fiddle with that
whole USB stick "persistence" thing.
Regarding your trouble installing Trisquel, it looks like you still haven't
posted the information on /var/log/syslog. That's probably important for
understanding what's failing. I've successfully installed Trisquel 6 on four
computers (one of them 32-bit), so I have a strong tendency to think it's
something about your hardware that's the problem.