£800 first build - gaming

[JJ UK]

I have a budget of around £800 give or take and want to build my first computer. I wanna get the best I can for my money and as this is my first build really don't know what I'm looking for - looking for some wide suggestions on what is best for my money etc.

I have a monitor and a TV which I will play from (both running at 1920x1200)
I have Surround speakers which run from USB and right now I can handle using the keyboard and mouse I have - apart from that and a 7 - 8 year old PC that struggles to run Age of Empires I need everything

Thanks in advance guys!

 

[JJ UK]

Also forgot to mention that I MAY be using 3DSmax in the near future and if so would like to be able to run comfortably on this setup too

I will be needing a new OS but that can be omitted from the price for now, thanks guys!