Resizing the vhd ok, but the windows don't start!

[aredhel vlsi]

Hello I am new at the forum, I had my Windows working for a long time, until I got this problem, resizing the hard disk. After hours of trying hard to resize my disk via terminal I managed to do this (I am not used to using the terminal):

1) I copied the windows XP.vhd to the location VirtualBox VMs.
2) I wrote on terminal :

A) VBoxManage
B) sudo VBoxManage modifyhd /Users/aredhel_vlsi/"VirtualBox VMs"/"windows xp"/"windows XP.vhd" --resize 40960

You see, I never imagined that it needed quotes because of the gaps in the words, at first it didn't recognize the command.
So it worked an I got it resized (I show progrees in percent at the terminal) .

I also checked that in VirtualBox I get the 40GB.

But the point is when I start the VirtualBox it shows me FATAL ERROR ! The windows don't start at all. If I try to add the copy of my old vhd, it shows me an error that it can't copy it. What can I do, please help me ! I can't show you the messages I get because my jpg files exceed the limit permitted for uploading. I also can't show you links to get an idea, because I am new to the forum and it's not permitted either. Obviously, I need help .

Please do not post a big guide becuse the more I read the more confused I get. Is there any way to at least restore the old capacity in MB so as to run my windows again? Thank you in advance !

[mpack]

The only way to reset the VHD to its original size is from a backup. You say that you copied the XP.VHD file from elsewhere, so I assume you are able to do that.

Was this VHD part of a working VirtualBox VM? (if so then I wonder why you chose the inferior VHD format over the default VDI).

Did you use snapshots in the VM? If yes then resizing the base image is pointless anyway, since it'll have no effect on the current state.

[aredhel vlsi]

Thank you for your answer. I don't remember why I chose vhd, I am not an expert on Virtualbox, I just wanted a simple way to have windows on my mac. I followed instructions from a video, and it was not clear if I had to chose vhd or vdi. Yes, it was a part of a working VM. What do you mean " Did you use snapshots in the VM?" I have a file Snapshots that is empty.