Mac Mini Freezing Issues

Question

So, I recently bought a refurbished Mac Mini, late 2009 model. It worked fine for the first few months, but after moving back to school, it started acting oddly. First, it had problems booting. It would freeze up during the boot up, or occasionally right after if finished booting. After messing around with it, it started working fairly reliably again. However, every once in a while, under moderate use, it would freeze up and would have problems restarting. I came to the realization that it was probably overheating, and tried a few tricks to get more air to it. This worked…
For a while. Last week, it died. It would get to the gray screen with the spinning wheel, and then freeze. It couldn't get past this step. In desperation, I took it into the Apple store, as it was still under warranty. After several days, they fixed it, but in the process, had to replace the hard drive. Luckily, I had a back up. Reset the computer, reloaded the back up, and started to use it… only to have it freeze again.
I noticed that every time it crashed, it seemed abnormally hot. I think this may be an overheating issue, and I have taken steps to monitor it (I currently have a temperature monitor watching over the CPU temperature). I just wanted to know what other people thought.
My current set up is thus:
Late 2009 Model Mac Mini, 2.53 GHz Intel Core 2 Duo
Dual monitors, connected via adapters to the Mini-display port and mini-DVI port
Ethernet internet (limited wireless here in the dorms)
Apple keyboard and Logitech mouse
Verbatim external hard drive, 320 GB, connected via Firewire 400/800 cable
My current thoughts are that it's either due to the dual monitors stressing out the video card, or the external hard drive. I've noticed that the external hard drive is constantly on when it's plugged in to the computer (it gets it's power via the firewire cable), and that if I leave the external drive plugged in overnight, the computer can occasionally act sluggishly.
If anyone has any further insight into this or can verify my hypothesis, that would be great. Thank you for your time.

Answer 1

After looking around online some more, found that there are many complaints with this specific hard drive. The main issue, it seems, is that it has limited ventilation, and therefore has issues staying cool. Unfortunately, due to the length of my firewire cord, the external hard drive typically has to sit fairly close to the Mini, usually resting on top of it. So, if this is right, then it's the poorly designed external HD overheating, which in turn overheats the Mini to the point of failure. I'll look into getting a better external to replace this one, and for the time being I'll only have it connected for brief periods for backup.