1. your problem will be easy to diagnose if you specify your mainboard model, cpu, what os 32 or 64
2. dual or triple display limitation are based on hardware also software config.
3. first thing you should know is
3.1 who are you (all hardward that you built)
3.2 how to know --> read all info about your hardware (eg. mainbord operation manual)
3.3 after you know yourself, you know your limit, what you can, or can't. and why can't

Alright, let's get to the point,
my comment based on Intel's Dual Display limitation for 2nd gen cpu architech

What you are connecting can't be  accomplished because your "DVI to VGA Convertor"

you can't use 2 x vga (analog) display at the same time (dual display)


Your DVI Port is "DVI-D" (D: digital only, dual link type)
that's why your display can't be detected.


"D-Sub, DVI-D and HDMI monitors cannot be enabled at the same time.
You can only choose the combination: DVI-D + HDMI, DVI-D + D-Sub,
or HDMI + D-Sub'
info source: H77 Pro4/MVP Specification [Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้http://www.asrock.com/mb/Intel/H77%20Pro4MVP/?cat=Specifications
PDF Manual Download: [Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้http://www.asrock.com/mb/Intel/H77%20Pro4MVP/?cat=Manual

DVI: Digital Visual Interface: [Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้https://en.wikipedia.org/wiki/Digital_Visual_Interface

Edit: DVI Wiki's info added, link fixed
Edit: "D, Referred to Digital only" changed to "D: digital only, dual link type"