Disable smart option in the bios and reboot. If that fails, as the computers detecting the hard drive it boils down to MBR damaged or faulty hard drive. Boot from a floppy and check to see if you can see all the files on drive c (unless ntfs format), if you can see the files/folders etc re sys the hard drives boot sector e.g sys c: and then type fisk /mbr once finished reboot, Now if that fails then it's likely to be the hard drive that's got corrupted or has failed completely.
Post back and let us know the results.
BullDog(UK)