Yeah not to gang-up on the OP, but he needs to know $500 is a budget build. Ham Louis seemed to be getting to the idea that he could save some money and use it for better-quality hardware if he could, for example, reuse the Power Supply, or the case, or at least not have to buy a monitor. Maybe beg for some parts from some friends. I happen to have about 7 cases, and 3 power supplies and would LOVE IT if someone would knock on my door and ask for them for free, because I can't bring myself to just throw them away and they aren't worth enough to try to sell them on craigslist.
Some basic questions need to be answered.
1) Can the OP get away with onboard video? If so, then he can save some serious money not having to buy a video card.
2) I recommend buying an Intel processor because it can usually (but always you have to check) come with a heatsink and fan. That's a savings.
3) If the OP can find a free case (I find them all the time on the side of the road and in dumpsters), that will save the cost of the case and the $$ to ship it. Cases are big and heavy and expensive to ship.
4) If the OP MUST buy a PSU, the Seasonic PSU 80+ certified is a must-have. There's a small series of them, for about $50. One as low as $40. Never, ever, ever, ever, ever go cheap on the PSU. Ever.
5) Never go cheap on the PSU.
6) Just don't do it. It's really dumb.
7) Make sure to get a good-quality PSU, like the Seasonic I just recommended.
8) Stop ignoring me. Don't go cheap on a PSU. I don't care how much you are tempted to save $10.00.
9) NewEgg has the best parts search features on the planet. If you are looking for a defined set of parameters (example 2 X 4 Gbyte DDR3 RAM, listed from lowest to highest price) NewEgg is the only place in the world to shop.
10) Anyone that disagrees with #9 is an idiot, and once they declare themselves, you should ignore everything and anything they ever say about anything except for perhaps the best way to spell "potato".
Here's a budget build I did the other day:
$292.74. It's REAL rough in the sense that I didn't think of EVERYTHING. There may be compatibility issues. It was done in 2 hours mostly as a proof-of-concept. I wanted to know how cheap I could go and still maintain a minimum level of quality. Every single part in the build could be upgraded (with the increase in cost that goes with it). This is an abstract starting point.
Note the Seasonic PSU. You can't beat that thing right there. Best part of the whole build. The memory was meh, because once you get any faster than that, the cost jumps up exponentially. As Ham Louis mentioned, OP needs to research minimum specs for the software he wants to use.
1) List softwares
2) Post specs for each
Example you might get a software that requires more than 8 Gbyte RAM. 12 maybe. Or it might want a minimum quality video card (and NOT onboard). The time to find this out is BEFORE you spend money. I'd be interested in hearing from an AMD build advocate on why they think it might be better. The main reason I chose Intel was because their processors included Heat Sink and Fan, and I've used them and they work pretty good. And they are low so you dont have to think about whether or not there is enough vertical clearance. And also that motherboard can upgrade it's processor all the way up to i7. I don't know if you can upgrade a motherboard with a low-end AMD CPU all the way up to it's top-of-the-line CPU, but if you could that would be a good argument.
My personal interest in a possible AMD vs. Intel competition for a budget build is which generates the least amout of heat. It used to be AMD's ran cooler than Intel, but that was back in single-core days and I don't know if that's still true. So an argument for AMD might be that you get same performance, same cost, HSF included AND it runs cooler. And maybe a foot massage too.
Another probably upgrade could be an SSD, which I think personally is also a must-have, but on an ultra-low budget build I kept it off. I like the new SSD's that plug into the PCI slots. They have much faster read/write times, but a 250 Gbyte Samsung EVO would be good too. Depends on how huge the OP's data files are going to be.
Another good question.
@OP: How many drives in your current system and how much in round numbers data is on them. 100 Gbytes? 500 Gbytes? 2 Tbytes? This will determine if you can use an SSD, a single large standard HD or one of each maybe.