VM doesn't work anymore

[oldchook]

I've spent days now trying to get the VM (Windows X on Mac OS Mountain Lion) to work again after a day when everything "froze" on the previously well working VM, e.g. nothing responded anymore.
In desperation I finally uninstalled everything (via the uninstall tool), deleted all VM related files, rebooted the Mac and tried to re-install VirtualBox from scratch. I always get stuck at the moment when the Vbox tries to install the VM, it always comes back with an error message: FATAL. No bootable medium found. This happens with the Windows XP installation CD in the DVD drive, or in choosing a virtual disk and trying it with an *iso file of the Windows installation.
I then tried to recover an older version of the VirtualBox with the Windows XP VM from Time Machine. The recovery process seemed ok but now I get this error message:

Machine UUID {cf20e95a-b9b8-4854-9a38-23b3bfe5bbf7} in '/Users/xxxxx/VirtualBox VMs/Windows XP/Windows XP.vbox' doesn't match its UUID {c8ad4926-3584-4bda-80fb-ca77e69a0185} in the registry file '/Users/xxxxx/Library/VirtualBox/VirtualBox.xml'.
Result Code:
NS_ERROR_FAILURE (0x80004005)
Component:
Machine
Interface:
IMachine {5eaa9319-62fc-4b0a-843c-0cb1940f8a91}

What the heck does this mean???? What am I doing wrong? Help please! Please give any comments in layman's language, I'm not that well versed in computer speak.