Inspiron 3847 graphics card

One of the Dell 3847 in the office is having video problems. This is a stock machine with build in graphics, a 4th gen i5 3.2G, with nothing on any slots. It is discoloring and showing horizontal flickering. Extensive Dell diagnostics said everything is just great. Reinstalled Windows from ground up made no difference. I am now convince there must be some kind of hardware video problem (tried different cables and monitors), what Dell diagnostics said notwithstanding.

Machine is less than 3 years old and everything else appears to be fine.

I am looking for a cheap video card to see if it makes any difference. Recommendations?