JJ,
Not sure I completely understand the problem, but can you get to the 'run command' ( start/run ) then type in :
scanregw /fix
If not and you can get a DOS C prompt, type in:
scanreg /restore
and see if you are presented with  RBcab000 ( XXX ) with dates, the highest number cab will be the last one.
Or maybe you can do a search/find for :
rb000.cab.
They will be found in directory c:\windows\sysbckup. browse to that directory. See how many total copies of rb00*.cab files there are. The RB is registry backup and should contain 4-5 backups with dates, if not the highest number is the latest.
From there you should be able to restore it.