You must be rejailbreaking the phone aren't you?
It happened to me first time as well.
It kept crashing when it got to uploading ramdisk.
I followed a few fixes and applied them all at once, so I don't know which one works. You'll have to try them all.
When restoring your iPhone as new for the clean jailbreak, make sure iTunes recognises the iPhone in recovery mode. This is done by powering off the phone, holding the sleep button for 3s, then press home for 15s, then release sleep.
Once iTunes recognises it in recovery mode, start the restore by shift clicking the restore button and choosing the fw.
Other possibilities are run redsn0w as admin.
And setting the redsn0w process affinity to CPU1 only.