I doubt the engine has seized. Believe it or not, the distinct possibility exists that you starter packed it in. Try what Will suggested, but I bet the starter is toast. AS to the rough idle etc, check the OVP relay. Known to cause this type of problem..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.