Your are using system restore correct? Since the 'undo' is incomplete, this might mean that your backup is corrupted. Try using a different backup if you have one.
Hope this helps,
It might be due to your anti-virus program. turn off the protection,
restart the pc and press f8 till recovery menu appears.
select repair computer
then follow steps which will lead you to numerous options for recover
now restore your computer from here.
I am sure it will complete the restore.