It's more of a never done it want to do it project, I want it to play games but I'm not a gamer so it doesn't need to be ultra setting or anything. I want it to be fast, I wouldn't mind it encoded video at a decent rate, I wan't it to look cool because I'll probably give it to one of my boys when I've finished. It's also worth mentioning that I have hard drives laying about also optical drives and a rather decent if not dated gigabyte HD5670 1gb card. Budget around £500 as I said I don';t want to throw money at it it's more to keep me busy.
With AA and AF turned off, the HD 5670 is able to play COD MW3 at 1440x900 with a playable frame rate. The HD 7770 will get you a slightly better frame rate at the same resolution, but will allow you to have AA and AF turned on too.
If you have some mechanical storage capacity already, I'd drop the hybrid drive in favour of a pure SSD solution. Hybrid drives are a compromise aimed at laptops and small form factor (SFF) PCs.
Taking that into account I'd suggest:
Asrock 970 Extreme3 Socket AM3+ 7.1 Channel Audio ATX.. | Ebuyer.com
AMD FX-8350 4GHz Socket AM3+ 16MB Cache Retail Boxed.. | Ebuyer.com - For pure gaming I'd have suggested an Intel solution. But because you want to do video encoding the 8 core (4 module) chip in the AMD will perform better than the quad core i5-3330.
Kingston 8GB (2x4GB) DDR3 1600MHz HyperX Genesis Plug.. | Ebuyer.com - Gives the CL9 timings at 1.5v rather than the 1.65v needed by some DDR3 1600MHZ DIMMs.
Crucial v4 128GB SATA 3Gb/2.5" SSD | Ebuyer.com - Not a top of the line SSD, but good brand, decent price and a 3 yr warranty.
XFX HD 7770 Core Edition 1GB GDDR5 Dual DVI HDMI.. | Ebuyer.com
Coolermaster Elite 430 All Black Case With Elite 500W PSU | Ebuyer.com - doesn't look that much different to the case you chose, and comes with a decent 500W PSU (estimated system power draw ~300W).
For video encoding, if your budget had been around £600, I'd have suggested the i7-3770K + Z77 chipset. For example:
Lists | Ebuyer.com
Not only is it overkill but PSU in general are more efficient at high loads so using a 750W PSU in a system that is likely to draw around 150W is actually worse then a 400W PSU. Something like a i5 with 8GB RAM, 1 SDD, 1 HDD, midrange video draws around 250W at full load so a 500W PSU would be ample even allowing for future upgrades.
Anything more than 20% load on an 80+ certified PSU
should still be over 80% efficient. But, yes, the old load:efficiency sweet spot around 40-60% still exists.
Take the Corsair TX 650, for example:
I didn't actually get round to calculating it, but that's the site I tend to use too.