unable to format local disk C

there it is

Please post back a screenshot of your maximized Disk Management drive map and listings:

1. Type Disk Management in Start Search box.
2. Open Disk Mgmt. window and maximize it.
3. Type Snipping Tool in Start Search box.
4. Open Snipping Tool, choose Rectangular Snip, click New, draw a box around full drive map and all listings.
5, Save Snip, attach using paper clip in Reply Box.

Tell us what is on each partition.

Were you not aware you are to boot the WIn7 installer to install it? If you're installed on D it is because you incorrectly ran the installer from another OS. Do you still have another OS on C?

Righto Wolfgang - just asking for the fuller DM screenshot to confirm all the flags..

C is clearly System holding the boot files, which is why it won't format and likely had/has an OS he ran WIn7 installer from.

D has Win7 as signified by boot flag but can't host boot files since it's Logical. So he can either convert D to Primary to claim the Win7 boot files allowing C to be formatted, or leave the C boot partition as it is having a data partition host the boot files.

I would myself either reinstall WIn7 to C or if he wants Win8 install it there which itself would take care of the 7 boot files by configuring a Dual Boot.

whs said:

It is hard to tell because you did not expand the upper field called "Status". But it looks like your C partition is the System partition which contains the bootmgr.

Please check that. Expand the field "Status" and see whether it says "System" and "Active". If that is the case, deleting the partition would make your system unbootable. Post back and we'll tell you what you need to do.

this is enlarged image .

Kaktussoft said:

Your bootmgr and bootmenu are on C!! How did you install WIN7?? It looks drive letter C was already in use when installing win7. So not done by booting by win7 install DVD. Did you install WIN7 when booted in another win7/vista/winxp?

As greg told you ... first convert D (your win7 partition) to PRIMARY with partition wizard.
How to set partition as Primary with partition manager?
Post screenshot of disk managment afterwards

When i was using xp it was installed in C but after that i have installed 7 in D and formated XP which was in C .