First, some brief history. My main computer - which we'll call Computer A - is getting up there in age. Most of the components were purchased around 2009. The video card is a bit newer (a few years old at this point). For the past few months, I had a strange problem when playing games in fullscreen mode. The screen would become rainbow patterned with a ton of multicolored lines. This would go away once I switched to Fullscreen-Windowed mode, though. The desktop was fine. It was only when launching a game in fullscreen mode.
Fast forward to a few weeks ago. Suddenly, even games in windowed mode were being distorted with the rainbow lines. Not only that, but now the entire desktop was being distorted. What's even stranger is that, after starting the computer, the brief BIOS display logo (I think it's the ASRock logo) would display correctly and even the little Windows 10 startup animation would display correctly, too. It was only when it got to the desktop that it would get distorted with those rainbow lines.
OK, fine, I think to myself. Let's start isolating variables. I did a fresh install of Windows 10 to a new SSD. The following are my results. I have a second computer to compare to and I'm plugging these computers in to two different locations (my house and the office at work at) for testing purposes.
Computer A (my main) hooked up at my house - RAINBOW GLITCH
Computer B (an extra) hooked up at my house - DISPLAYS OK
Computer A (main again) at the office - DISPLAYS OK!!!???
What possible reason could there be for Computer A to glitch out at my house but not at the office? And remember, Computer A displays fine (at my house) up until it gets to the desktop. The motherboard maker logo (ASRock) and the Windows 10 loading animation both display properly. And even a different computer altogether works fine at my house on the same monitor with the same HDMI cable. It's only once Windows 10 loads completely at my house on Computer A. All other computers and locations are fine.
There's only one more variable I can think of and that's my speaker inputs. At home I plug some powered speakers into the back of Computer A. I plug these same speakers into the back of Computer B, though, and it displays properly. Could there be some interference from the speakers in Computer A that isn't there on Computer B? I have not been able to test this out yet. And I doubt it's even the problem due to the BIOS screen and Windows loading screen displaying correctly.
Help!