Is there a white sticker on the motherboard with a PBA, something like:
E74800-xxx (S3420GPLX)
E74801-xxx (S3420GPLC)
E84395-xxx (S3420GPV)
E85654-xxx (S3420GPRX)
? Or, if it's another number, post it here and I'll see if it is an older variant of one of the above.