Probably NTFS problem.
Check to see if you have the jumper incorrectly set on the wrong pin of your hard drive... or that an EIDE cable is bad... gently unplug and re-plug all cables, and power.
However, It is likely that the Windows floppy does not find the drive because it is formatted in NTFS format. To run fdisk, you have one choice that will enable you to bypass that limitation of no partitions found. I think it is the fourth choice on the lsit, but then you would need to do a full reformat to get Windows back on there.
If those do not work, it is likely your hard drive is bad... but I doubt that.
How valuable is the data on that drive?
I called HP who told me there are no longer restore discs for that model, but that if your drive is the original, you can access the drive to make a new install set as soon as you can see your screen.