Re: Firmware dowload crashes NXT
If the battery charge is marginal, downloading firmware can fail because the voltage is not "strong" enough for writing to the flash memory to succeed. So replacing (or charging) batteries can often solve rebooting problems.
If the reboot fails in the middle, you may have to use the "magic" button to force the NXT back into original boot mode.
To isolate this to a NXT, battery or ROBOTC issue you can try downloading the standard NXT-G firmware. If this properly downloads and reboots and ROBOTC firmware does not then it would seem like a ROBOTC issue.
If you're still having troubles, please report again. Or send me a direct email at email@example.com
to see if there is a way to help out.