While I don't have experience flashing (once I cash my insurance in though, I will
) if you aren't sure it's done, you could always just go to bed. If you wake up and it's not done, it's probably not working.
I'm not sure if this information would be useful to anyone who might help you, but, posting the device and what you are flashing to could be beneficial. Or at least get someone a bit more interested in helping if they can identify with the problem more.