If you have not setup the partition to be a MS-DOS partition see other possibilities. A save to partition utility such as Phdisk is present on the hard disk drive. This utility is designed save information you may be working on when it goes into sleep mode or when your battery becomes low on power. Generally this partition will be a small section of the hard disk drive and you should have another partition setup as a Primary or Extended Logical that contains your Operating System. If you do not have a laptop or all partitions are being dis played as a MS-DOS partition refer to another possibility.
Computer virus is present on the computer.
If you believe that none of the above possibilities are causing your computer to be displayed as a MS-DOS partition it is likely that the computer may be infected by a computer virus.