Michael
You can't have on-board, and real video card working at the same time. It's either this, or that.
When you install real video card, on-board video is either automatically disabled (newer cards), or has to be disabled in BIOS.
I don't think, you have to go back to the shop, and I don't see anything wrong with shop people. Maybe they saw on-board video failing, and that's why they recommended real video card.
BTW, real video card is always better, then on-board video. In most cases, it has better specs, than on-board video, and what's more important, it doesn't use computer's memory (RAM), because it has its own RAM.