I don't know about high settings but you should get by with medium settings with the video card , I would be more concerned about the power supply not the wattage but the quality, sounds like something from bestbuy.
Yes and no.. You have a decent foundation, but I'd make a couple changes, if you only paid $590 for the whole rig, you won't be out too much.
Theres a couple "no no's":
Power supply, this is a major cause of concern. You basically have a no-name generic power supply. Unfortunately this is a common mistake first time builders make. They buy premium components and then use a cheap power supply to drive them. The power supply is easily the most important choice to make. Low quality power supplies can kill your CPU/Motherboard fast just from being defective and a quick overvoltage. OR, they can kill them slowly with their piss-poor voltage regulation.
I would suggest getting something like a Corsair TX650v2, yes they're expensive, but quality is the reason. A good power supply can easily last you 10 years, you can use it for a future build, and the Corsair TX series power supplies have a 5 year warranty.
The 5750 is a couple generations old, but it should be fine if you're playing 720p. Its not a great video card, even when it was new. If you find performance lacking, I'd suggest dealing with that.. AFTER, the power supply (you'll get tired of me saying this by the end of my post)
The case and lighting is kinda..... eh.. Honda Civic with a huge spoiler and underbody lights? LOL, but if you like it, thats all that matters.
Motherboard, if you have any aspirations to overclock that CPU (and yes, the FX series processors are known to be able to hit well over 4.0GHZ with an adequate cooler- and theres no reason not to), I would suggest a higher quality motherboard. That mobo is not the best for overclocking on, and ultimately the CPU is only as good as the board its sitting on.
A decent CPU cooler to overclock with would run you about $30.. I would suggest a CoolerMaster 212 Evo. Definitely resolve the power supply issue before attempting to overclock.
Keep those suggestions under your hat if you have some extra cash after x-mas.
I would agree that Dynex PSU has to go. The PSU is one of the most important components. If you have the money I would go for a more up to date GPU and after market heatsink/fan as the stock fan can get quite loud. Other than that it looks good. The FX-8120 is really a good CPU despite what a lot of people say. I have a FX-8120 in my system and can tell you I can play every game there is at ultra/max at 1080p with no problems.
Change out the PSU and GPU and you will have a very good system.