Indeed 2 partitions. system boot manager/bootmenu is on OS partition. In bootmenu is an entry to start from same partition. You only have 1 option so it isn't diaplayed. Partition 25GB isn't touched at all in boot proces! Only if booting with special key to enter ASUS recovery mode.
You tried reformatting and recover to factory settings already. So no important files are on disk (or at least backupped already?