When I got a new computer I formatted the disck into 4 partitions.. and 40 gb was left over from 160 gb. Now I want to reactivate that 40 gb unused space.. jelp me tell me how to do it.. I tried the diskpart and got the below message..

C:\>diskpart

Microsoft DiskPart version 5.1.3565

Copyright (C) 1999-2003 Microsoft Corporation.
On computer: WIN2006

DISKPART> list volume

Volume ### Ltr Label Fs Type Size Status Info
---------- --- ----------- ----- ---------- ------- --------- --------
Volume 0 C NTFS Partition 20 GB Healthy Boot
Volume 1 D Giga Drive NTFS Partition 39 GB Healthy System
Volume 2 E NTFS Partition 39 GB Healthy
Volume 3 F NTFS Partition 29 GB Healthy

DISKPART> select volume 1

Volume 1 is the selected volume.

DISKPART> extend

DiskPart failed to extend the volume.
Please make sure the volume is valid for extending.

...tell me how to do it..

See How to extend a data volume in Windows Server 2003, in Windows XP, in Windows 2000, and in Windows Server 2008 (http://support.microsoft.com/default.aspx/kb/325590). Note that extension for basic volumes requires that the unallocated free space must be the next space on the disk following the volume to be extended and be contiguous. So you can either backup E and F, delete E and F, extend D, recreate E and F, and then restore E and F using diskpart and a backup utility, or use a 3rd party disk partitioning tool to extend D in place and not have to deal with E and F manually.

But if you can give me method of doing it as I am not know how to do it..

.. if you can give me method of doing it ...

I provided two in my previous post, the first was:
1. Backup the data on E and F using a backup utility of your choice. Windows includes a backup utility that has built-in help information for using it.
2. Delete E and F using DiskPart.
3. Extend D using DiskPart.
4. Recreate E and F using DiskPart
5. Restore data to E and F using whatever backup utility you used in step #1.

If this is unclear, perhaps for the sake of your data, local assistance should be sought.