Arma 3, bf4, minecraft, and dayz. I don't know anything about pc but I want to get one soon. I have about 1300$ to spend.
What kind of pc is needed to play these games?
For minecraft you need
CPU: Intel P4 or its AMD Equivalent (AMD K7)
RAM: 2GB
GPU: Intel GMA 950 or AMD Equivalent with OpenGL 2.1 Support
HDD: At least 100MB for Game Core and Sound Files
For bf4 you need
Dual core CPU (Intel Core i5 or AMD "Bulldozer").
At least 4 GB main system memory
Graphics card with at least 512 MB of VRAM and support for DirectX 10
30+ GB of harddrive space
Windows Vista
For arma 3 you need
OS - Windows 7 / Vista
CPU - Intel Core i5 or AMD Athlon Phenom X4 or faster
GPU - Nvidia Geforce GTX 260 or ATI Radeon HD 5770, shader Model 3 and 896 MB VRAM, or faster
RAM - 2 GB
HDD - 15 GB free space
DVD - Dual Layer compatible
DirectX® - 10
And for dayz you need
OS - Windows 7 / Vista
CPU - Intel Core i5 or AMD Athlon Phenom X4 or faster
GPU - Nvidia Geforce GTX 260 or ATI Radeon HD 5770, shader Model 3 and 896 MB VRAM, or faster
RAM - 2 GB
HDD - 15 GB free space
DVD - Dual Layer compatible
DirectX® - 10
Personally i'd recommend an i5 or 7, with 8GB+ RAM with a generally decent graphics card.
Just a heads up, DayZ isn't quite stable yet and even ultimate gaming rigs can suffer from frame drops on it.