Projector Ground Loop

I've got a unique set up and need advice on how to best set up for safety without causing a ground loop. My Projector (Optoma HD65) is installed on the ceiling. There is a standard looking power outlet on the ceiling which is powered by a long cord that runs through the wall into a closet and plugs into a normal outlet in the closet (this plug has three prongs including the ground). Then my projector plugs directly into this outlet on the ceiling which is powered by this long cord into a closet plug. There was also a component cable through the wall and into a closet (so using a switch box for all my equipment). The problem is when I plug in the projector to the ceiling outlet I get very visible horizontal scrolling lines on the screen. Therefore, I took a three prong to two prong adaptor and removed the metal ground piece on the adaptor and FIXED the problem...no more lines! However, I've read this is unsafe, but the Outlet it's plugged into is powered by a three prong plug...so is it still grounded safely or not? If not, any thoughts on a simple solution to this? Thanks!!

I moved into a house last year that had the wiring already installed. I'm just learning about it and want to do it right and get the correct wiring in my home - it appears to be a bit jerry-rigged. It sounds like there may be some wiring issues so I'll get it checked out by an electrician. appreciate it, thanks!