My system hard disk shown as emty

If you have installer disk handy,

Versions 10.9, 10.8, and 10.7
Boot into the Mac OS X boot loader menu by holding down the OPTION key at system start

• Choose the Recovery drive to boot into recovery mode and wait until the "Utilities" screen appears
• Pull down the "Utilities" menu and choose "Terminal"
• At the command line, type "resetpassword" without the quotes
• Confirm the new account password, then reboot the Mac as usual

Versions 10.6 and 10.5

• Insert the bootable DVD into the Mac and restart or start the computer
• Boot the disk by holding down the "C" key at system start
• Select your language preferences and then under the "Utilities" menu select "Password Reset" (it may say "Reset Password" instead, depends on theversion of Mac OS X)
• Select the hard disk that the forgotten password is on, then select the username of the forgotten password, you'll then be asked to select a new password
• Reboot as usual from the hard drive, using your newly reset password as the login!

Run the Check Disk Utility.

To run the check disk utility you will need a repair disc or a operating system disc. Put the disc in the cd drive and boot from it. You want to get to the Dos Command Prompt (Black screen with white letters) and type the following command: chkdsk /r
Check disk will run well over an hour or two and you will notice the percentages going from high to low, this is normal. Let it run to completion. Then reboot machine.

If check disk fails to solve your problem you might have to reinstall windows. Try doing a Repair Install that way you don't loose your data, documents, music, pictures, videos or programs.

In windows xp you get to the dos command prompt by selecting R for repair when the options appear.

In Vista and Windows 7 you want to get to the recovery console and look down at the bottom of the window for the Dos Command.

Run the Check Disk Utility.

To run the check disk utility you will need a repair disc or a operating system disc. Put the disc in the cd drive and boot from it. You want to get to the Dos Command Prompt (Black screen with white letters) and type the following command: chkdsk /r
Check disk will run well over an hour or two and you will notice the percentages going from high to low, this is normal. Let it run to completion. Then reboot machine.

If check disk fails to solve your problem you might have to reinstall windows. Try doing a Repair Install that way you don't loose your data, documents, music, pictures, videos or programs.

In windows xp you get to the dos command prompt by selecting R for repair when the options appear.

In Vista and Windows 7 you want to get to the recovery console and look down at the bottom of the window for the Dos Command.

If your hard drive shows as empty, you should be able to reinstall your operating system from the system disk.
If the disk has failed, though, it will not accept the operating system. You'll have to buy a new hard drive.
In a Dell computer, if you press the special function key to select a boot option (I think it's F12), one option should be diagnostics. Here you can test the hard drive. If it comes up with an error, you'll know for sure what the problem is.

This error occurs when the PC hard disk has error(s) and your using particular software as you have mentioned like partition magic. To solve this problem shut down all your applications and running software.
If you are using Windows XP
Go to Start>Run>In the run box type cmd
A black Window will open its called CLI or Command line interface. In this Window run the following command on the C partition CHKDSK /F if the message appears"Check the system next time the system restarts (Y/N) type "y". then type "d:"to enter D partition. When the D prompt (D:) appears type the same check disk /Fix command which is "CHKDSK /F" and hit enter.
Similarly repeat this command for all the partitions.
If the this option statement appears "would you like to force dismount on this volume? (Y/N). Select "Y".
If you are using Windows Vista or Windows 7 then when you perform the first step which is Start>Run>In the run box type cmd before hitting enter in the start menu look for a small black icon named cmd on the top of the start menu. Right click it and select "Run as Administrator" When the black cmd window opens all the steps after that are the same as described above.

Good Luck!

yes
if you are logged on the computer
click on start-settings - control panel - administrative tools - computer management
expand users group
right click on administrator - click on set password
and leave all textboxes empty
click ok
and ... that's it

Run an Error check on your computer. Process takes anywhere from 1 to several hours, depending on hard drive size, files on computer and number of errors needing to be fixed. Manual steps to run Chkdsk at the command prompt loadTOCNode(3, 'moreinformation');

1. Click Start, and then Run.
2. In Open, type cmd, and then press ENTER.
3. Use one of the following procedures:
   • To run Chkdsk in read-only mode, at the command prompt, type chkdsk, and then press ENTER.
   • To repair errors without scanning the volume for bad sectors, at the command prompt, type chkdsk volume:/f, and then press ENTER.
     
     Note If one or more of the files on the hard disk are open, you will receive the following message: Chkdsk cannot run because the volume is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts? (Y/N)Type Y, and then press ENTER to schedule the disk check, and then restart your computer to start the disk check.
   • To repair errors, locate bad sectors, and recover readable information, at the command prompt, type chkdsk volume:/r, and then press ENTER.
     
     Note If one or more of the files on the hard disk are open, you will receive the following message: Chkdsk cannot run because the volume is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts? (Y/N)Type Y, and then press ENTER to schedule the disk check, and then restart your computer to start the disk check.

if you right click on my computer --> manage --> disk management

does it have a valid driver letter that does not conflict with any other drives ( drive letter assignments ) ?

Also if you right click on it and go to properties and go to tools and run a check disk on it ?

That or you can go to command prompt ( start --> all programs --> accessories ) or start --> run and type

cmd

Then click on ok or press enter and type chkdsk X:

where X: is the drive letter of your usb drive with the colon ie :

The hard drives ready for failing, back up everything now to avoid loosing data, run chkdsk /f this command will scan the disk for any problems and try to fix any bad sectors, if this doesn't work i'd think about buying a new hard drive

when you get into utilities in F2 command, the hard drive should be able to be shown by highlighting the first boot device line and then pressing the up or down key, or the + or -keys or pageup/page down key,to change the selection it will be there it is just not selected.