The computer may not "see" the drive for many reasons, some of them to cope not happen, you will need a competent specialist. However, if you know the reasons such problems, it is possible to protect yourself from rash action.

The main reasons for such problems

Most often the hard drive is not recognized in the BIOS, that is load with him, something impossible. Confirm your assumptions can be, if you boot from another device, e.g. another hard drive or CD by going to "computer Management" select "device Manager" and search for the desired disc. If the car "sees", then the problem is in the BIOS. In turn, the hard drive in the BIOS could not be determined due to the violation of the connection of the power cord and interface cable. The fact that the power unit moves several cables: one connected to motherboard other to hard drives. If the HDD power cable is not connected properly, the "system unit" will continuously light the indicator.

The same problem may occur when the incorrect location of the jumpers, switch the screw in the desired operation mode. It also happens that jumper at all. The most common situation, when not detected the SATA hard drive. It can help reset the BIOS. If the PC does not "see" the hard drive is IDE, then you can check the inclusion of the controller in the BIOS.

Reasons why the drive isn't recognized in Windows

Most often, the system does not see hard drive when properly exposed the priority of the boot properties in the BIOS. For example, in the characteristics, responsible for loading the operating system, the first number is the CD-ROM and second hard disk. In this case, if the drive contains no bootable disk, and any other system will not recognize hard drive. Not the right external hard disk drive may due to excess current in the USB ports of the computer. This situation is typical in case of USB connection of a large number of peripheral devices used for information exchange, and to obtain power.

The machine can not find the hard drive due to a faulty power supply. If she makes loud, unusual sounds when you restart, it is likely that she lacks the power of the power supply. The reason why the computer does not detect second hard drive, could be a wrong cable connection or a conflict between two drives of the same brand.