Processors come in a variety of shapes and sizes (literally):

Low End - This group is slower, cheaper and will do for most basic programmes. However, is that what you want your pc to do? Processors have fallen dramatically in price (£35-£50) for the basic model and the higher end scale. Of course no matter what you buy it will be out of date very quickly.

Mid range Processor - Probably the most popular on sale at the moment. Prices tend to be in the region of £70 - £120 and will comfortably handle most programmes nowadays. However, if you are building a machien to play games on you want a high end processor to deal with the immense power required for graphics.

High End - The most expensive and by definition the quickest. Balance what you can afford with what you need your pc to do. In three months time that processor will be at least half the price it is now.

For current prices see E Buyer

Which CPU you need for a new system is clearly a matter of personal choice and based in the main on what you can afford. Connected closely to this is that you will also need to purchase a heatsink cooling fan (don't confuse this with the general cooling fan for your system-you need both). Some companies will sell a "set", whereby this is included. CHECK before paying out on another.Make sure the fan is of the ball bearing variety and not a sleeve bearing fans - put simply these are rubbish. Read the documentation also, to check that it is suitable for your processor and won't be overwhelmed by it.

Never carry out any work on your computer whilst is is plugged into the mains power socket, you could cause yourself and your PC damage.

The power supply does not contain any user servicable parts and contains hazardous voltages it should not be opened-even after it has been switched off.

Many desktop and tower cases have sharp edges be careful when working inside the case of your PC.