You need to look at what has happened to the partition table. One of the tools like partition manager should allow you to see what has gone wrong although you will have to boot from some other media first.
Choices exist in the BIOS to boot from whatever bulk storage devices your motherboard supports. Compact flash drive for instance.
In fact ISTR one way you can get into trouble like you describe is leaving non-bootable removable media in a drive slot that is recognised as potentially bootable by the OS and is given priority by the BIOS.
ISTR it would manifest itself as something like drive J too.
It might be just a case of either removing media from a slot or altering the BIOS settings to always boot from the primary drive.