Looking to upgrade my desktop PC

[Jarek Mace]

Hello ladies and gents, my computer is a lot older than a year now and I think that the old man is in need of a dusting and an upgrade. Sadly, I'm not all that when it comes to computers so I'm going to need your lovely advice.
I'm willing to spend up to £500, so I'll need your advice on what parts to buy and upgrade my PC with as well as where from, bare in mind I don't want to use newegg because I'm from the UK.
Thank you!
EDIT: I'm also looking for a set of decently priced but good gaming headphones and a new gaming keyboard, if you could recommend any, cheers.
Here's the rundown:

Case COOLERMASTER ELITE 310 BLUE CASE
Processor (CPU) AMD PHENOM II X2 555 (3.20GHz/6MB CACHE/AM3) - BLACK EDITION
Motherboard ASUS® M4A78LT-M: mATX MAINBOARD, DDR3, USB 2.0, SATA 3.0Gb/s
Memory (RAM) 4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Graphics Card 1GB NVIDIA GEFORCE GT430 PCI EXPRESS - DirectX® 11
2nd Graphics Card NONE
Memory - 1st Hard Disk 640GB WD CAVIAR GREEN WD6400AARS, SATA 3 Gb/s, 64MB CACHE
2nd Hard Disk NONE
RAID NONE
1st DVD/BLU-RAY Drive 24x DUAL LAYER DVD WRITER ±R/±RW/RAM
2nd DVD/BLU-RAY Drive NONE
Memory Card Reader INTERNAL 52 IN 1 CARD READER (XD, MS, CF, SD, etc) + 1 x USB 2.0 PORT
Power Supply 350W Dual Rail PSU + 120mm Case Fan
Processor Cooling STANDARD AMD CPU COOLER
Sound Card ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)
Network Facilities ONBOARD 10/100/1000 GIGABIT LAN PORT
USB Options 4 x USB 2.0 PORTS @ BACK PANEL (MIN 2 FRONT PORTS) AS STANDARD

 

[evilneko]

Upgrade your cpu fan and experiment with overclocking? Try out the whole dual video card thing, assuming your mobo has a slot for one? Honestly, I don't really see a reason to upgrade that thing except for bragging rights.

 

[Supernova1138]

I would try unlocking the two extra cores on your CPU, see if it runs stable with the unlock. If not, look at getting a Phenom II X4. Don't bother with dual video cards with the one you have. The GT 430 is really low end, and getting a second one for SLI (if you mobo supports it) won't give you good performance. You'll likely run into lots of microstuttering issues, along with all the driver and game issues SLI/Crossfire tend to have. Get a better single card instead.

If you do get a better graphics card, you'll probably need to get a better power supply. If it is a generic power supply, or it came with the case, it probably isn't of good quality. A good quality 500 Watt power supply will run just about any single GPU system. Antec, Seasonic, Corsair, XFX, and Enermax are good brands.

As for what to spend on a new graphics card. For a good worthwhile upgrade look at something like a Radeon HD 6850 or 6870, or a GTX 560 on the nvidia side. If you can find a GTX 460 with a 256 bit memory bus, that would also be good. The 192 bit version that is more common is inferior to the 256 bit 460, and the 6850.