You must have OFW 4.00 stored somewhere. On you internal or an external drive.
You installed OFW 3.40 at first, from the disc. Then you some how installed 4.00.
When installing firmware, you should always remove the disc and any other usb devices. Except for the usb you are using to install.
And you should have definitely not accepted the update, when you seen it said 4.00.
Well, this time when you downgrade. Follow my guide below. and you will be all set.