IPhone won't update to 4.0, sync/back-up

Question

I have an iPhone 3G, version 3.1.3 (I connect to iTunes via an HP PC). I have tried several times to update to 4.0 but it doesn't work. It seems to get hung up on the back-up process. I click Update, it goes through the process showing the progress bar that shows the repeatedly moving little green boxes. It then has a box that says Backing up iPhone with an empty progress bar. After awhile the progress bar then shows one green box and this is where it seems to get stuck (I've also tried just syncing/backing up by right clicking on the device and selecting from the menu and it does the same thing). I've left it for more than an hour and it never moves any farther and it doesn't update to 4.0. Does anyone have any idea of what the problem/solution might be? I've never had any issues in previous updates/syncs.

Answer 1

Had the EXACT same problem and found a workaround.
It turns out that, while syncing doesn't work when updating to iOS4, it still works if you do it manually in iTunes. So sync your phone normally with iTunes in case something goes wrong.
Then download this little program: http://www.microseconds.com/backupswitch.html
It will allow you to chose whether you want iTunes to perform automatic syncs or not. Make sure you've quit iTunes, disable automatic updates through backupswitch and re-start iTunes. Now chose to update your iPhone to iOS4 and you will be told that there was an error and iTunes will ask you if you want to update without syncing. Click "accept" or "yes" or whatever it was and voilà - watch iTunes update your iPhone!
If you like, you can then re-enable automatic syncs through the backupswitch program.
Hope this is helpful and good luck!