Hey. I am clueless to what is causing this. I am using Windows 8.1 64 bit, and whenever I use it in normal mode, my PC will randomly freeze, and I mean completely random. It can range from 10 seconds to 3 hours before it freezes. It never freezes in safe mode. This happened when I replaced my hard drive because I was receiving a reboot and select proper boot device error. I spoke woth Microsoft about this, and they said that it is a GPU issue. Replaced the GPU, still freezes. They also said to reinstall Windows. I did that, and now it freezes upon setup. I also replaced my motherboard, CPU, and DVD drive because of unrelated errors. I have updated the BIOS, reseated RAM, Windows Memory Diagnostic, updated drivers, malware removal, etc. Please keep in mind that I currently cannot access my OS, since it froze during installation. Please help. Could it be because of a hard drive change? Myold hard drive is a Seagate Barracuda 1 TB st1000dm003. The new one is a Barracuda 1 TB ST310005N1A1AS-RK.