Do I need to upgrade my computer?  It runs well but it's rather old and I'm putting a fairly heavy load on it.  What I've got now is a home-built computer, Windows 8.1. 
Processor:  Intel Core 2 Duo CPU   E7400  @2.80 GHz  2.27GHz
Installed memory (RAM):  4.00 GB (3.25 usable)
System type:  32=bit Operating System, x64-based processor
Pen and Touch--No pen or touch is available.
Motherboard: Gigagyte  (I don't know what model)
Gigabyte Graphics card, AMD Radeon HD6670  2GB  DDR3
500 Watt power unit
237 GB free of 278 GB
I've got 12 projects so far, each between 70-100 MB, for a rough total of over 900 MB.  It runs 13 minutes so far.  But my plan for the movie is much larger--it should be roughly 30 minutes with lots more projects.  Everything used to run perfectly but recently when I put all the projects together in my Corel Video Studio Pro X4, after 10 minutes or so the screen suddenly goes dark.  When I left click the mouse, the screen lights up again but the action has stopped and I have to click the start button.  The movie resumes from the same place where it stopped and then finishes.  Each time I play the movie, the movie stops at a different place, but the movie always stops some place before finishing.  Could the problem simply be that the screen-saver automatically activates itself after about 10 minutes or so, which makes the screen go dark? 
Also, I didn't try to render anything yet but I'm worried that it will render at a crawl or maybe not have enough power to do any rendering.
So, do I need to upgrade my computer?  If so, what do you recommend? I'm only an amateur, not a pro, and I'm on a limited budget.  (I'm not planning to get iClone 6 but even if i did, I guess that it would not improve my situation).

it depends how much you add to your scene,  the more shadows and such that need to be calculated in real time,  the more stress your computer will endure - sometimes some cad type models can cause a lot of stress to iclone. which for reference,  the stress really comes from the video card,  if the video card can't keep up with the amount of information iclone is capable of causing in real time,  the video card crashes iclone from the blockage - which also consider,  this is real time,  that is a huge amount of data to process with little space for buffers,  which would only lag the scene. DX12 is expected to be a game changer for amd users though,  so let's see if that's the next evolution to take real time animating up a notch.

you can do a great movie without having to upgrade your computer,  but upgrade your work flow and use older hollywood techniques -  such as rendering your scene in parts and layering them in your video editor.  Trying to do huge scenes in real time,  is not the proper way to do things -  mainly because technology isn't there yet overall and the extreme control you would need to add more high grade nuance to your scene, would more appropriately be handled in layers,  hence your workflow. 

Ask not how much iclone can do for you,  but how much you can do "with" iclone!   ( which is a lot, if you handle your project the right way in the workflow )

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Thanks so much for the information, Planet Star Dragon!
It's very helpful, but I still wonder about why the movie stops after 10 or 11 minutes when I view it in the video editor.  If you think that the persistent stopping of the playback in the video editor is nothing to worry about then I can relax a little.   (As I said earlier, I don't have one or two large projects that might overstress everything.   I already have been layering many small projects (each 70-100 MB) into the video editor). 

I use to get errors like that when I was editing with uncompressed avi files.  These days I just render from iclone to mp4.

chances are your video editor is lagging like that from the stress it's putting on your cpu.  The cpu does the file decompression in the system,  if you have a heavy format,  and the cpu is struggling to keep up with decompressing the file in real time,  you will get those type of errors.    You may also want to check your video editor set up options,  see if it has an option for "Hardware acceleration"   and turn it off , or maybe even on,  usually "on" can cause problems - but this is also an observation from using an nvidia gpu with an intel cpu -     you have an amd gpu so reactions may vary. 
Again,  this is another issue that can be solved through workflow -  meaning ,  the highest resolution you can get in a render is printing to image -  you then take those images compile them in your video editor,  then have your video editor compress it to the best native format for editing.  different systems and softwares can have different results so mileage may vary there as well.   The idea behind adjusting your workflow,  is to be able to do things manually that would require less processing power .....BUT usually requires more steps to break down the project into smaller, easier to handle chunks of data.

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Thanks again, Planet star Dragon!
I turned off the Hardware Encoder Acceleration, as you suggested, and for the first time there was no stop in the playback in the video editor! (The Hardware Decoder acceleration was already turned off).
Cheers!

Dada