Help I'm trapped in an infinite loop and I can't get out

Like a complete genius, I put this in the startup program:

while true do
  shell.run("power")
end

Which seemed fine at the time, except now I need to edit something. Here's the fun part: when I try to terminate the program, it will terminate power, and then immediately restart it. The turtle has a label, so breaking him will not work, and I'm on a SMP server, so I don't have access to the files. Help?

Put it next to a diskdrive with a disk which has a do-nothing startup (ensure the drive is not on a side with a peripheral). Computers prefer to boot from disk over local files unless otherwise specified in the config.

Open the computers UI, press control-T and hold it (for a second if I recall correctly). This will terminate the current program and return to the command prompt. (Another one to remember is control-R, used in the same way, to restart the computer.)