After cleaning a computer from malware I decided to double check there wasn't a residule MBR virus by running MBRCheck. I followed the steps, and received the message "Found non-standard or infected MBR". I followed the steps to repair the MBR with the standard Vista MBR (yes the computer definitely had Vista installed). The operation completed successfully and I restarted as instructed. Unfortunately after the BIOS I received the message than no boot record was present. After restarting a few times with my fingers crossed I slaved the HDD to a different (and 100% functional) PC so I could backup the files. Unfortunately it reports the drive as uninitiated unallocated space. I connected the HDD via USB to my laptop and it reported the same thing.
I have already posted to Majorgeeks here
specifically to ask for help recovering the files from the HDD. As MBRCheck comes from this site I felt I would be prudent to post here for more information on MBRCheck and in particular whether there is a means to undo it's changes?