my hard is Hitachi [250.05 GB]
laptop:dell vostro 1520
my hardware not low format
error is :Unable to lock device. Make sure you do not have open files on this device and try again.

please help me

That error message usually means what it says - Windows has open files on that disk, and so the program cannot obtain exclusive access to it. For example, you cannot expect to run that utility to erase the disk which Windows boots from, or the disk where the Windows swap file is (if different to the boot disk) etc.

Thank you for respond my question

Please give the iso file software..

Download Hitachi ISO from:

Hitachi Drive Fitness Test v4.16

There are loads more Boot CD ISOs out there, Hiren's, Ultimate, etc., etc., but as it's an Hitachi why not use their own tool...

The manual can be found HERE

The prog can't lock the drive as Vulcan said because you're using it to run the program and windows is constantly accessing it, use the Boot CD above or a DOS Boot CD with LLF capability for your drive, and you shouldn't have any problems low level formatting your drive.

S

I have two sata HDD installed. In Your opinion WIN7 is constantly accessing form the C:drive the other drive D:. HDDLL is installed on the C: drive.
It is drive D: I like to Low Format. It's unable to that in WIN7. Why should I use HDD low level format!

Do you see drive in Computer in windows? If you see it you have to get rid of letter for that drive. Otherwise FS is still mounted, which would prevent you from formatting whole drive as windows would lock any mounted partition (and whole drive as well).
Control Panel (sorry I have no win7 at the moment) - find administrative tools - disk management - remove drive letter for drive, which you want to format.