I very much recommend a self-built PC. I have built 2 from scratch so far, and they both run beautifully. Your money is much better spent on parts than on a pre-built.
Basically, you start with the processor and motherboard, P55 is a good chipset for a budget rig, and then pick an Intel i5 or i7 that is the same socket as the motherboard. The socket is will be something like LGA1156 or similar. (You could also start with a processor and pick a mobo, it doesn’t matter). What you pick is based on how much money you’d like to spend. The mobo could be picked based on features you’d like, such as integrated sound, a specific number of PCI-e slots, PCI slots, etc. Just make sure it will work with the processor. The CPU can be chosen based on a trade off of how much speed you want compared with how much you wish to spend. Generally, the higher the number of model, the faster the processor.
Next, find some RAM that is compatible with both the CPU AND mobo. This is critical. Timings and speed is not as important, but you should get at least a 4GB kit, that’s pretty much standard for a modern PC. Most mobos can automatically set the timings for the RAM so it will work, and that will be fine unless you are a real enthusiast. Usually, you can look up the list of compatible RAM memory for the CPU and mobo very quickly on the manufacturers website. You might even find a package deal on Newegg or something.
After you’ve got those 3 important pieces, the rest is really easy. Get a video card that will fit into your budget, a PCI-e one (make sure your mobo has at least 1 PCI-e slot). That’s really up to preference whether you want Geforce or Radeon. Radeon’s tend to be cheaper, but the Geforce drivers are more “mature”. In addition, you will need to get a BRAND NAME 700, 750, or 1000 watt power supply (750w would be just fine) such as Cooler Master OCZ, Thermaltake, etc. Make sure it has the proper power connectors / enough power connectors for all your peripherals and your video card.
Lastly, you will need to find a case that everything will fit in, again, up to user preference. As for cooling, the standard CPU cooler that comes with the CPU will be more than enough unless you plan on overclocking it (which I’m guessing you won’t). You don’t need anything fancy like watercooling. You could by fans and a fan controller if you wanted, but they aren’t REALLY necessary.
Anyways, the most basic modern computer should have the following (my recommendations in brackets):
-Motherboard (I’d suggest P55 like my rig)
-Processor (Multi-core, >2.5 GHz)
-Compatible RAM (~4GB )
-Video Card (>512Mb)
-Power supply (Brand name, 750W)
-Case (user preference, I have a CM 690II and I love it)
Anything else you buy is up to your budget.
Here are my specs (a bit old, but it runs anything) for reference for ya, and how I chose each: (Prices were in CAD)
MOBO: Asus P7P55D-E Pro Socket LGA1156 (This one I picked cuz it had 2 PCI-e slots for SLI/CrossfireX) ~$150
Processor: Intel i5 750 (Was the largest i5 I could buy at the time, quad-core, plenty of power for my needs) ~$225
RAM: OCZ Obsidian DDR3(RAM type, mostly everything uses DDR3) 4GB kit (Not sure of exact specs, RAM changes very quickly) ~$120
GPU: 2x Sapphire Radeon HD5770 1Gb (I picked these because they were cheaper with decent performance and I read that they ran cooler than other cards) ~$200 each
PSU: Cooler Master GX750W (I like Cooler Master, and 750W was plenty good enough. I picked this PSU because it has one voltage rail which outputs about 60 amps, I like this for Crossfiring the 2 cards together. Most PSU’s have 2 rails with lower amperage which don’t work as well.)~$120
CASE: Cooler Master 690II Advanced (Personal preference, I like the outside and the black painted interior, the hardware is nice and it’s big enough to fit my stuff. Fairly high quality. There are a lot of lower quality cases out there, be careful) ~$100
And that’s it. Total is ~$1115 CAD (About $1200 USD currently) and as I said before, it works like a dream. Of course, you probably can’t get these parts any more, but you get the idea.