In order to reboot your iPhone, press and hold the sleep/wake button, and move the slider to shut the phone off, then press the same button, to boot your device again. Restart your computer as well. Once the devices are on again, try to update or restore again.
If the new version of iTunes is available, make sure to get it, and install it on your computer. Often, such a simple solution is the one you have been looking for.
If the previous solution did not provide any results, remove the software from your computer, and then, install the latest version all over again.
There is a chance that firewall or your antivirus settings are causing the problem, by blocking the connection. Make sure to check those settings.
If your security software is not up to date, that might be the reason why you are struggling with the error 3000 now. Update it, and check if there is any difference.