A system depreciates the moment you bring it home, exactly like a new car.
An OEM, proprietary system like a Compaq is even worse, as after three years there may not be any kind of driver support, and there might be a new operating system on the market you'll want to run. And these kind of systems rarely have a decent cooling solution, which greatly decreases the functional life span of the internal components.
An experienced user is going to realize this, and take it into account when you are ready to sell. And each year, it's going to become more and more difficult to find someone inexperienced enough to buy the system just because of the brand name.
Let's suppose, hypothetically, that this is a Presario 8000 system that costs an even three grand at this moment. In a year, that could depreciate to as low as $750.00, or a quarter of the initial purchase price. In another year, less than half of that.
I'll swap you a middle-of-the-road video card for that $3000.00 dollar computer in three years to sell as a first system for a child, and that would be because you're my pal, and I feel bad that you were stuck with a Compaq desktop for three years. Unless you upgrade the components while you own the system, and with an OEM machine, you may discover some exasperating limitations in that area as time goes by. Not to mention a hot markup on the Compaq prices vs ordinary retail. We won't even get into wholesale prices ... I don't like making people irritable.
I'll undoubtedly also base my decision on making the swap on whether I can do anything to improve the system, such as adding a new video card, a cooling fan, and if the PSU needs replaced. If replacing a part isn't cost-effective, you might end up donating it to a local school to take it off your taxes. Because I just won't be able to bring myself to buy it from you.
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I had a customer bring me a Compaq he bought two years ago from Radio Shack. He had paid $1200.00 for the system. I took it in trade to help pay for the labor when I built his new system, which cost three hundred dollars less than the Compaq, and is many, many times faster.
I added a 128MB stick of SDRAM and a fan, and sold it to a neighbor for $50.00.
I felt kinda guilty, because I made a profit. But business is business, and I made no bones about what he was buying. It was good for getting on the Internet and checking email, but not much else. An 8MB integrated video card doesn't allow for much in the way of modern games, and the motherboard had no AGP slot.
It was junk, IMHO, especially with a Cyrix processor ... but better than nothing.
Remember, you asked for my best guess!
Toejam31
<font color=red>My Rig:</font color=red> <A HREF="http://www.anandtech.com/mysystemrig.html?rigid=6847" target="_new"><font color=green>Toejam31's Tantalizing Tantric Toy</font color=green></A>
<font color=red>Second Rig:</font color=red> <A HREF="http://www.anandtech.com/mysystemrig.html?rigid=15942" target="_new"><font color=green>Toey's Dynamite DDR Duron</font color=green></A>
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<font color=purple>"Procrastination on your part does not constitute an emergency on my part."</font color=purple>