E510 Hard Drive Not Found on Boot (But Only Sometimes) All OEM

I have a Dell E510 (Dimension) with Windows Media Center XP.  I bought it when they first came out, like last November.  It's a decent but not overwhelming system.   For the first time ever on my Dells, I did not buy the extended warranty so it ran out after 90 days.  It has the 160GB hard drive (SATA).

 

For maybe the last 7 or 8 months, when I restart the computer I sometimes get the "HARD DRIVE NOT FOUND" or "PRIMARY HARD DRIVE NOT FOUND" error.  I then reboot again and sometimes it works fine, sometimes it provides the error again.  The most times I've gotten it in a row is 3 before it booted successfully the next time.  I usually can reboot 6-7 times successfully before I get the error.  When it boots, the computer works wonderfully.

 

I have done some research.  I've made sure all power and connection points are snug.  I've taken the hard drive out and made sure it wasn't damaged (visibly).  I've done some Google searches also.  One indicated that perhaps the hard drive is spinning too fast and it's not getting read, but I couldn't find any way in the Setup to adjust the hard drive speed.  I've also gone in through set-up and made sure everything is configured properly, and it looks to be that way.

 

Does this sound familiar to anyone?  I want to get a newer model so I'd like to sell this one but don't feel comfortable selling it until I have a grasp of this issue.  Part of me thinks maybe the cord, part of me thinks maybe the hard drive.  When it boots, the hard drive is very reliable.  I have also done a full Scan Disk and defrag on it at least monthly.  It's well protected by pc-Cillin and SpyBot.  I don't want to waste my money replacing the cord or drive if it's a configuration issue but I highly doubt that as I never touched anything on the Setup menu until I started getting the error.

 

Help!  Anyone have any thoughts?