Ok, a new build (~3 months running, and not used very often) has been booting up extremely slow lately.  I started trying to diagnose the problem today and here are the symptoms:
 
• Slow on startup (Windows XP screen, specifically)
• Random lockups
• RealTek Audio sometimes randomly says "cables unplugged"
• When attempting to do a Western Digital Diagnostics extended test or HD Tach test (specifically in the sequential read test) CPU is pegged at 50% and status bar moves REALLY slow
• During WD diagnostics extended test the 'current sector:' jumps erratically instead of sequentially
 
Here are the specs:
Athlon 64 X2 4000+ Brisbane
Gigabyte GA-MA69GM-S2H
2GB Adata DDR2 667
WD 1600AAKS SATA HDD
Samsung ODD
FSP 450W PSU
 
I was thinking at first the OS install might be corrupt or something, but I'm starting to think I need to get everything off the HDD and RMA the thing before it dies on me.
 
Help.
 
Kyle

Backup all your data (It never hurts) and try a complete refformat (not a quick one), then a chkdsk, if some bad sectors come up go ahead with the RMA.

A full format includes the chkdsk, that is the only difference between a quick and full format.

@KyleSTL, make sure the disk controller hasn't changed from DMA to PIO mode. Run memtest86+ for grins.

Hard drive problems are very hard to diagnose with Software tools.

 
A full format does a full read scan of all sectors on the drive.  Chkdsk can optionally do this with the /R parameter, but by default, it doesn't.  Chkdsk's main purpose is to make sure the file system pointers, directories, and MFT all have consistent data.  During a format, there is no file system on the disk, so chkdsk wouldn't have anything to check.

If he is trying to mark bad sectors on a drive. The a full format will do the job, running Chkdsk would be redundant. This is from MS:
Differences between a Quick format and a regular format

 
If he is concerned about a failing drive he should go into the BIOS and turn on SMART. Also, SpeedFan has a nice SMART tool included. I suspect the drive is good but windows has some conflicts. Maybe he should try a restore, depending on when he noticed the problem.

Tried restore to ~3 weeks before symptoms, no change.
Ran Memtest, it was fine.
 
Did an image copy to an extra hard drive in a second computer, threw the backup disk into the machine and it booted up just fine.  Ran DBAN on the system disk (the 1600AAKS), and did an image copy back from the backup in the second computer, threw it back into the original computer and it's slow booting and very unresponsive again.
Note: the backup drive is an IDE disk, whereas the primary drive is SATA.
 
Is there a possibility it's my MB (northbridge issue or something)?
 
I'm going to reload WinXP tonight (after another DBAN run) and see if it fixes the problem.

Update:
Attempted to ran DBAN again on the disk and the program says:
"DBAN finished with non-fatal errors.
Errors are usually caused by drives with bad sectors"
Before it even gets to the interactive mode screen.
 
I think I found my problem.  RMA time.  Thanks for your help, guys.

I'm still not convinced that you have a bad drive, check the SMART in SpeedFan.

Oh yeah, the smarts are all ok.  I reloaded Windows on the drive and everything seems to be flying.  No hangups, slowdowns or any of the original symptoms.
 
Is there a chance it could be the NB?  Corrupt data?  Funky MBR?
 
I'm going to leave it like this for a while to see if the symptoms come back.  Anyway, even if the drive fails I still have its exact image on the backup drive, so no data loss.

You ran a memtest with no errors so it's more likely it was you. It happens all the time. You load a driver or some pigsh!t and things don't go well in windows. It's hard to find that stuff. I install anything I want on a whim (except real player ), and every once and a while I have to spend a couple hours figuring out what I pigged up and removing it.

Well, in that case, at least it's not a hardware issue.  I would try to RMA myself but I hear God takes forever and there's a lot of red tape.  Thanks for a guidance.