Overall, my PC runs faster than you would think at 7 years old - mainly because I have had more RAM put in and a new video card recently, also about 3 years ago it had a new Motherboard as well. This PC is faster than my sisters brand new Windows 8 laptop, too - shocking, I know.
In the long run, £330 + would be okay, no more than £400 though. I really would appreciate your help finding me a decent new PC, preferably a Dell because that is my favourite brand of PC.