Your suspicions may be well founded, especially as you have tested your bootable device on another machine. You could boot to a Live version of Ubuntu and run a memory test to determine that it's your system memory generating the problem.
Depending on your results and/or your patience, you might also be able to use trial and error, removing one memory module ...
The GPU is a Graphics Processing Unit. From here, you can check what the gpu is approximately doing. In web browsing the gpu can help decoding video's, but the CPU (Central Processing Unit) gives tasks to the gpu and if it doesn't, the gpu will be silent and just draw pixels.
Well, The GPU is working With the CPU. While intense graphicing when the CPU is overloaded or is not detected/compatible, the GPU activates.
But mostly the GPU is just working on shaders and the CPU the scripts.