Getting insert boot media errors, maybe it's the hard drive?

The new rig I built for my parents kept giving me insert boot media messages and it was sometimes a hit or miss if it threw it. Then one day it just worked but not it's back to giving the errors. Is it possible it's the hard drive? I mean I tried switching the IDE cable from the dvd drive to the hard drive to see if that was it and changed the jumpers around on it, still nothing. And the ide to sata converter that was on it was the thing that originally gave me the problem. Then it came back and started working, now it's out again. Do you think it was the sata to ide converter or the hard drive? The dvd drive works fine on the IDE, just not the hard drive. This hard drive is around 10 years old or older. Think it's just dead or something? It's a WD 250gb IDE.

What are the chances it's the hard drive? I'm about fed up with this and just want to get it working so they can stop hounding me day and night and rushing me and all this other ****. I found a WD Blue 320gb for $50, think it'll do fine for the rig?