Knacked battery, it was running on the main lead only. May even be a flat cmos battery as well.
Try starting it in 'safe mode' (sounds like it may already be in that though) if you can try doing a reset with the system restore, if that fails and you have the wherwithall then take HDD out and piggy it onto another machine as a slave drive and get your data off it. Then stick it back in, put the recovery disk in and re-boot with that. It will overwrite everything but with luck sort it.
This posting may have been helpfull, on the other hand probably not... Either way, I may have had drink when posting it in which case it's probably not as helpfull as it could have been
Work safe, and remember all technical problems can be resolved with a hammer, the trick is knowing where to hit it and how big a hammer to use (I often find it may also help to have a spare bit in the shed to replace the bit you have just mullered

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