No Monitor image after installing GPU

So this is my first build ever, been basically using newegg YouTube channel as a guide, and answering specific questions with Tomshardware google searches. Now I have a problem that hasn't turned up results in a search, at least not good ones.

So here goes: I put together everything EXCEPT the GPU and it's been running great for one day. I installed Windows and started up my Steam library downloads. Today I put in my GPU (AMD 7870 Sapphire non-OC version) and now I have no image. Everything starts up fine, the fans are going (GPU fans too) and I've double- and triple-checked my cables...I'm 99% sure nothing is hooked up wrong.

Some specifics: My monitor is DVI or VGA only, no HDMI option. I only have a VGA cable so I've got the monitor hooked up to only the motherboard since the 7870 doesn't have a VGA output. I'm wondering if this is a problem, does the monitor HAVE to hook up to the GPU? I feel like I should still be able to use the motherboard VGA to output images...maybe it's a driver problem? There is a Sapphire GPU driver CD that I haven't installed yet. I'm gonna try that next and will edit this.

If anybody has any other ideas, they would be greatly appreciated.