Don't bother with the manufacturer's tests. They only tend to tell you when the drive is actually failing, imo. Whereas there are utilites that can surface scan the drive to show you its state so you can see if you're going to be running into problems in the future.
Download a copy of MHDD 4.6 from hddguru.com, burn it to CD (or use the floppy version if you're so inclined, it has the same functionality). It's free.
Make sure your drive is set as master if it's an IDE drive then boot from the CD/floppy.
Select your drive from the list by typing the corresponding number next to it, hit F2 to identify it, then hit F8 to see the SMART stats.
If the RAW figure for Reallocated Sector Count, Current Pending Sector Count, or Reallocation Event Count is higher than zero, then the drive is throwing up bad sectors. Replace it.
Hit F4, then F4 again to run a surface scan. 3ms, 10ms, 50ms blocks are all fine for a modern drive. 150ms indicates a little slowness reading a specific block but isn't bad. 500ms means the drive is having issues reading a block which will probably be reallocated if it gets worse.
UNC, IDNF, AMNF, T0NF, any of those and backup your data and get yourself a new drive.
The only thing to note with MHDD is it doesn't always find drives. It's not a brand new program and it hasn't been developed in a long time (years) so it doesn't always work with some modern combinations of hardware.
If it doesn't detect your drive, then:
- For IDE/PATA drives, make sure the drive is set as MASTER and is the only drive on the cable.
- For SATA drives, try a different SATA connection on the mainboard.