Any decent deals on desktop pc? (£600 - £900 budget)

[ivrytwr3]

I am after a new pc as mine has now died

I do a bit of gaming and movie encoding and my budget is as per title.

Any decent offers on at the minute to get the most for my cash?!

I have seen:

https://www.overclockers.co.uk/ocuk-forcebox-express-intel-core-i5-6400-gtx-960-4gb-windows-10-fs-17i-ep.html

http://www.ebuyer.com/754096-pc-specialist-vanquish-vitrum-gaming-pc-pcs-d989406

http://www.ebuyer.com/749221-pc-specialist-vanquish-impact-iii-gaming-pc-pcs-d966682

No self-build and require a fitted CD/DVD drive.

Also, if i get a system with no OS, i have seen keys for £10 - how do i use a key to install a new OS (or can i not and need the CD/DVD?)

Ta!