Windows 8.1 64 bit
I just downloaded windows 8.1 and know my hard drive goes to 100% usage and and freezes every couple minutes I have 8GB of ram an AMD FX 4100 and a TB hard drive with 500 GB left.
Need a little more information like did you download it from the MS site or did you get it from somewhere else? And can you reinstall your old OS if your PC was previously working.
Edit: also since 8.1 is just a Beta release (which is prone to having problems) the OS is probably not fully equipped with handing your devices (like your hard drive). As i said before reinstalling your older OS should correct this problem and i would recommend using a virtual software program like: https://www.virtualbox.org/ for BETA releases or just trying out an OS without having to leave your current one.