What is wrong with my PC

I have an i5 4690k Stock no OC, 32 gigs of Ram and a Gtx 970. I shouldnt be having issues with this game but I am literally unable to play without buildings taking 3+ minutes to load and the second I press tab my whole computer locks up. Tabbing back in is impossible and I have to task manager it. I have defrag'd my Hard Drive and I have set the process priority to above normal, what else can I do?