First, research building a computer from scratch, although i know you don't think you could do build one by yourself; consider giving it a shot. Decide whether you would be comfortable doing this; its not as hard as one might expect, as long as you take the time to research and find compatible parts. The pro's of building a computer by onself include lower prices, more custamization, more originality, as well as more fun. In the future, knowing how to build a computer by yourself would be a reliable asset to have. negative aspects of building one yourself include: a certain level a risk and nervousness, which can be expeted but easily overcome, and the lack of a centralized company for tech support, meaning tha it many cases you must become your own tech guy.
If not, I suggest buying from either http://www.cyberpowerpc.com/
however, seeing that you live in Britian, I'm not sure whether these companies ship internationally. However, they both offer a high amount of customization, competitive prices, reliable support, and most importantly good build quality.
If building a computer, here are basic parts that are needed:
A CPU: Come in Single, Dual, Quad, and Hexa core varieties, built by either Intel of AMD. Both are good, but AMD parts tend to be cheaper and offer more chances in the future for upgrades. I would suggest AMD.
When selecting a CPU, take in account the socket type that it has. Recent AMD sockets include: AM2, AM2+, and AM3, with AM3 being the newest. Intel include sockets 775, 1156, and 1366, although 775 is starting to become outdated, and 1366 tends to run the highest level and most expensive processors.
When buying processors, the 4 main considerations are: socket type, company, cores, and clock speed. Many other, extremely important ones exist, but those are the basic.
Motherboard:More complex, but a necessity of the motherboard is for it to have a socket type of the same as your CPU. Also, if one wishes to play many games and such, buy a seperate video card, so one with onboard video is not needed. Also, onboard audio, in your price range, would be very helpful also; it will save money and complexity from avoding a seperate audio card. Go to sights such as Newegg.com to look at different motherboards, find advice, and read reviews for motherboards and computer products as a whole.
epending of the socket type of your motherboard, you will either have DDR3 or DDR2 RAM for your comp. First, off, AM3, 1156, and 1366 all use DDR3 Ram, which is the newest standard. The other sockets in this list use DDR2.
Next, decide on the amount; i reccomend 4gb of ram; although, giving your computer 8gb of ram would also future proof it for years to come.
Video Card: This is a very significant part of your computer when it comes to videos and games. Two mainstream design companies exiest: Nvidia and ATI, which is an offshoot of AMD. The choice depends on a matter of preference, with both companies offering a wide spectrum of products for many different users needs. Video cards i suggest for you are the ATI RADEON 5770, or the NVIDIA GTS 450; higher level of products include the NVIDIA GTX 460 or the ATI Radeon 5830. All these graphics cards, and modern generations as a whole, use a PCI Express 2.0 interface or socket, which is a fancy word for the plug in for the graphics card. Most, if not all new motherboards, will have this type of graphics card plug.
Case:They come in many different shapes and sizes, but offer a surprisingly varied effect on your computer, with different airflow and sizes; airflow is important for the getting rid of heat from the core componentes of a case.
There are two main sizes for the type of computer your looking at: Mid-Tower and Full-Tower. Unless your an enthusiast, I suggest a mid-tower, for cost purposes. Mid-towers fit ATX and Micro ATX, which is basically the form factors for an recent motherboard. Many different companies offer cases; many are good, some are best. Buy the best, it's worth it. Also, avoid ones that, however enticing it may be, include a PSU preinstalled in the case. Almost always these are low-budget and quality.
Power Supply (PSU):Power supplies are what every part of your computer is plugged into, and are then plugged into wall outlets, or hopefully a surge protector. Variations of PSUs include different wattage ratings and sockets for parts to be plugged into. I suggest, for your needs, one rated at about 600 watts and with 2 6-pin connectors for the Graphics Card. However appealing it seems though, this may be the worst part of your computer to skimp on. Bad PSU's often go bad, and/or damage other parts by way of heat or electricity.
Hard Drive: Fairly easy two understand, comparitively; a spinning magnetic disk that stores information on your computer. Two main variations here: capacity (how much data can be held) and RPM. Higher RPM and Data is better. I suggest a hard drive of at least 500 gb and 7200 RPM, which has become the mainstream speed. Many enthusiasts have begun to spring for Solid State Drives, or SSD's, which are miraculously fast...and expensive and low capacity.
Disk Drives: Easiest part; a drive in which disks are inserted. By a combo drive for both CD's and DVD's.
Monitors: Judged by size and number of pixels, little dots that form images on screens; most mainstream monitors will do great.
Keyboards and Mice: Easy; just buy fairly inexpensive ones unless you have a pressing reason not to.
Optional parts also exist: they include audio cards, for faster and more advanced audio and custom CPU coolers, which are quiter, more efficient, and cause the processor to run more cool.