I am running now with windows 8.1 32 bit. I have a disk with 64 bit that I would like to install because of call of duty ghosts requirement which requires 64 bit operating system. I have 3.20 gig amd phenom 2 x4 processor with 8 gigs of ram. Geforce gt620 graphics card with driver of 331.65. when I boot off disk to install 64 bit the screen looks horrible but was able to get the license key in to install but when it rebooted the monitor says it lost the signal and get a black screen. Don't know if it is the processor that is 64 bit ready or graphics card or what. Ended up putting 32 bit back on with no problems