I want a new pc but I don't want to buy it from alienware or anywhere else because I heard its a lot cheaper if I build it my budget is 1,500$ and lower.. Currently I have a horrible Nvidia 8500GT and 2g ram with 500g hard drive I want a pc to play crisis on very high with above 45fps and games like gta iv. Any suggestions?
I prefer AMD because you don't need to overclock it, but Intel tend to be a) cheaper and b) less power-chewing. It's up to you. You have a good budget, so there you go.
Then: What do you have now that you can reuse? Your hard drive is a starter - unless you have a gigantic music and movies library, you should be able to reuse it.
*How good is your case for cooling? Check it out. Use something like FanSpeed or another utility to look at your internal temperature after you've been running it hard - and give it a good clean to get the dust bunnies out first! The cooler it runs, the better. If it's not cooling very well, look at replacing your case fan with something more powerful, or consider a new case altogether if it is very old. There are a lot of good case fans out on the market; good cases are harder to find, but Antec make some nice quiet ones. Their Sonata series is very good.
*Disc drive - is it any good? I'm going to reccomend you get a DVD/CD combo drive if you don't already have one - most newer games are on DVD. Having burning capability isn't a necessity, but it's a nice bonus. There's usually not a big different between manufacturers and models - go with what you can afford. Blu-ray is pointless at the moment, though in a few years' time you might want to consider it.
CPUs are a bit contentious. AMD has a pretty decent range in the AM3 socket, so go with what you can afford. Intel I'm not familiar with, but I hear the i5 and i7 are good choices. Always go for a multicore over a single-core - they provide much more power. Stock fans will usually see you through, but if you've overclocked or your case is not particularly good for cooling, consider replacing the stock fan with a more powerful one. OCZ makes some good CPU fans.
For a graphics card, if you want to go the whole hog you can go with an ATI Radeon HD 5850, which is about $300-$400 depending on where you look. Anything higher than that is really just overkill. If you're looking at an Nvidia, consider some of the newer GeForce cards - the 9800GT looks good, or the 8800GTS.
Nvidia has a technology called SLI, and ATI's equivalent is Crossfire and CrossfireX. These allow you to use more than one graphics card in unison for extra power. In Crossfire, the cards need to be from the same series - so both from the 5000 series - but they don't need to be the same card. I'm not sure with SLI, but I think it works in a similar way. If you plan on doing this, look for a power supply that is SLI- or Crossfire-ready - this means it will have the right power connectors for the cards.
In terms of sound, see what motherboards are available for your CPU. Most have amazing onboard sound - my current mobo has support for 5.1 surround sound, and the one I have my eye on has support for 7.1 hi-definition. Sound cards are really only necessary if you're also doing heavy audio editing work.
Network is a contentious one. Are you gaming online or not? Online gaming will mean you'll want to look at a very good network card. I've been able to rely on onboard network capability so search around and ask questions if you consider going for a dedicated card.
RAM is very much dependant on your motherboard and CPU. DDR3 is the best choice, but check your CPU's specifications to see what it requires. You can get it in different frequencies - 1333 is the most common, but there is 1600 DDR3 available as well. Check all your other components to make sure they're all compatible.
Your operating system will determine how much RAM your system will be able to put to use - I'd say no more than 6GB and no less than 3GB, as a general range, but look up your chosen OS to see what its maximum RAM is. IIRC, Windows 7 can use 4GB in the 32-bit incarnation and 6GB in the 64-bit. Make sure you buy some sort of RAM cooling as well - it helps to extend the life of the RAM, and can be an absolute lifesaver if your system runs particularly hot. RAM fans are good and can look pretty too, but they draw power - not much, but it still take a plug from your PSU. Heat sinks aren't quite as efficient, but they make no noise and require no power. Make sure the fan or heat sink you choose will fit your RAM - and check to see if the manufacturer doesn't already provide a heat sink or fan with it. RAM kits are more likely to have cooling with them.
Last of all, the power supply. Find this last, because it's very dependent on what you chose earlier. Look at the minimum PSU requirements, and go with what it highest. Having a higher wattage PSU won't cause trouble, but it will go underused. If you plan to Crossfire/SLI your graphics cards, make sure that you check what the minimum requirements are to use that technology, not for a single card, as they're usually higher. Take into account any extra fans you're installing as well. Yo