>>>Can anyone advise me on what to look for
Er, no, sorry we can't!
That's not because we're being deliberately unhelpful but because you've not told us what you want to use the PC for!
If it's for top-of-the-range gaming you'll just about everything to be as good as possible. (e.g. a really fast processor, with loads of memory, an excellent video card and an equally good sound card).
If it's for professional video-processing you'll need much the same again (but with the emphasis being on a really good video card and a massive hard drive).
However if it's just for web-browsing, streaming videos, word-processing and playing chess on, just about any reasonably modern computer will do! Indeed, if those are the only type of requirements, I can easily recommend an excellent computer (from a firm I know to be outstanding):
http://www.accomputerwarehouse.com/product-info/budget-build-amd-2-8ghz-processor-2gb-ram-500gb-hdd-windows-7