1. http://www.google.nl/search?q=%22ntldr+is+compressed%22 gives possible solutions, but I'm afraid you might need a Windows XP CD to run them.

And if there were sector errors in a critical area of the harddisk, the only solution might be a total reinstall for which you surely need a XP CD. Better even follow the general rule for hard disks: if it gives errors throw it away. Do you still have warranty on this refurbished machine?

2. Maybe better contact HP for a cd at least? I don't know what you have and don't have.

3. For getting your data off, if necessary, see http://reviews.cnet.com/5208-6122-0.html?forumID=44&threadID=16394&messageID=181706 for a recommendation by one of the moderators. Note it's linux.

4. To safeguard your data: make regular backups to a removable medium. Don't wait until it's too late (like now, maybe). Hard disks can fail and do fail (Murphy's law: they fail at the most unwanted moment).