No signal on ASUS monitor

[hellohihello]

Recently, my PC had been refusing to boot. Long story short, I thought it was a motherboard issue, so I replaced it; turns out I was being a little too hasty in my diagnosis, since that didn't fix anything. As a second port of call I then took the GPU out and tried starting without it, and that did work -- the PC does now consistently turn on. However, my monitor is displaying "no signal" every time I start the PC. I'm using a DVI cable with a VGA adapter since the (new) motherboard doesn't have a DVI slot. As far as I can tell everything is plugged in properly. I'm really stumped, would appreciate any help on the matter.

GPU (not attached): Sapphire HD 7950
Mobo: ASUS P8Z77-V LX2
Monitor: ASUS VG248QE

 

[hellohihello]

Oh, some development. I put the GPU back in just for the hell of it, and the PC did boot. Not sure how or why. It wasn't doing that before, even though I tried very many times. Yeah, I'm rather confused at this stage. Startup repair did its thing, decided it couldn't fix it, then the PC shut off. Again, it won't boot. :S

 

[ffg7]

have you tried clearing the cmos without the videocard installed?