I get a 1720 Smart Hard drive detects imminent failure (Failing Attribute: B8) error on my HP EliteBook 6930p which has a Seagate hard rive

could be faulty harddrive.

Run a backup before the HD fails...quickest way to save all personal info.

go to hp website and download the latest firmware for your notebook

This is a warning that your hard drive will fail in the near future. It is wise to backup your data frequiently so you won't lose your data when the hard drive fails.
The faults your hard drive is experiencing will cause the computer to slow down as it tries to read and write data to your hard drive.
There is nothing you can do to fix the hard drive except to replace it when it fails.

This warningmeans the hard disk will fail sometime in the near future. You need to back upyour data regularly before the hard disk fails or you will lose your data.
When the hard disk fails, you need to replace with a new one and installWindows on the new hard drive to get your laptop working again.

Is your hard drive a Hitachi/IBM? If yes, Compaqs are known for their notorious hatered toward IBM/Hitachi hard drives. It's a compatibility issue over a quarrel Compaq had with Hitachi during the late 1990es. Or you may really be dealing with a dying hard drive. In either case, you'll have to get a new hard drive... or a used one but DO NOT GET A HITACHI. Get a Seagate or Samsung. It would be best if you transfer all your critical data off the hard drive and dont use your computer untill you get a replacement hard drive.

1. Try SAFE MODE first.
2 If the problem is still there, format the disk and reinstall XP.

Back up your personal files and buy you a new hard drive.

Sounds like your hard drive is about to pack up. You can disable SMART for your hard drive in your CMOS setup. which will allow you to boot up your pc. I suggest you back-up all your data as soon as possible before the hard drive fails completely.