When i turn the computer on, I get a message - 1720 SMART HARD Drive detects imminent failure. Failing Drive:SATAO Failing Attribute: # B8

SOURCE: I get a 1720 Smart Hard drive detects imminent

It means that the Seagate hard drive is near death. Backup all your data immediately, create a recovery cd starting from the recovery partition situated on your disk (if you haven't done this before or you weren't provided one when you bought it), replace the hard drive and reinstall.

SOURCE: 1720-smart hard drive detects imminent failure (failing attribute : 1)

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.