In that case, my suggestion is to take it to a shop and have a bench tech look at it. Having no knowledge of the system BIOS makes it tough to suggest any quick fix. Maybe the boot files have become corrupted. The instructions to repair the boot files and/or XP should that be the case require some knowledge of computers.
If you don't know what you're doing you can well make the situation worse when attempting data recovery. At the moment someone who knows what they are doing can probably recover your data (how much that will cost depends upon how it is lost), but attempt a bit of do-it-yourself and you may well put it out of reach for all time.