Late 2006 iMac Issue: Logic Board or Hard Drive? I have a question. I have a late 2006 17" White iMac, and it is having issues. I don't know if it has a bad hard drive (again..), or if it has a bad logic board, and I have no idea how to check it. I have taken this thing in many, many times for this same issue, but Apple just tells me it is a bad hard drive and just replaces it. Yet this issue continues to happen, and happen, and happen. I've been through 3 hard drives within the last three years or so.

Heres the symptoms: 
~Won't stay on longer than 10 minutes without getting the beach ball/pinwheel of death (as I have begun to call it)
~Or, it will freeze completely (if music is playing, the last note it was on will just endlessly repeat. 
~Screen will randomly go black with no way of getting it back. Only sign of life is a slight glow. 
~Hates more than one application open at a time, and especially hates Firefox/Safari/really any Internet browser... 
~Has bars and speckles of randomly coloured pixels in the display. 
~Sometimes will not finish booting sequence. 

What I have tried: 
~ I tried installing a light version Ubuntu, as I had no money for the newer versions of OS X. The problems only became worse. (As in, the keyboard/mouse no longer worked, everything was crashing, nothing would stay open, etc.)
~Following a million different tutorials that are supposed to "fix" the problem, to no avail.. 
~I replaced the hard drive. This didn't work, and now I don't even have any sort of picture (I do have the slight glow like I mentioned earlier) when attempting to boot from a disc. I have made sure three times now that I replugged in everything that I unplugged, and everything is where it should be. 
Is there any chance left for this poor Mac, or should I get my hard drive back and be rid of it? It is not under warranty, nor do I have any money to be able to buy a new logic board, and/or any idea on how to replace my existing one. I am not paying $700 to Apple for them to fix it either, as that is outside of my budget.

Any/all help with this is highly appreciated, and Thanks! (:
If the hard drive replacement method has continued to fail, I'd guess that either: A) The hard drive is not actually broken, or B) The computer somehow makes the hard drive go bad. I've taken that model of iMac apart before, and the inside is fairly cramped for space. That leads me to think that your processor may overheat and "hang", causing it to go black, or stop doing whatever process it's on and spin the "beach ball". If you really want to keep using your 9 year old machine, I'd suggest taking it to a repair shop that can repair Macs. They may find that it has a faulty processor or cooling system for the processor, or something else. I'm not sure how much that would cost, but in my opinion, it may be time to upgrade. Since you don't want to spend the price of a new Mac, you could look into purchasing a used computer. It's hard to transition to a Windows or Linux machine for some people, so if you've gotten used to Mac OSX, stick with it. I've seen advertisements for aluminum iMacs from 2008 or so for as little as $400 at local computer stores. If you're comfortable with Craigslist, you could look for one there, and it may be cheaper. However Craigslist doesn't have warranties. Read a little about purchasing a used computer before you do so.