How to fix PC reset problem

Recently, I replaced my motherboard, PSU, HDD, CPU and its Video Card. I reset everything and the new specs are:
From Corsair 750, I changed it to Thermaltake 850
From Z77Extreme 4, I replaced it with Z77Extreme 4
From Seagate, I changed it to Kingston 300v
From i5 2500, I upgraded it to i5 3570k
From MSI GTX 670, I changed it to old ATI 4870
My computer normally resets in BIOS than in Windows. I also purchased a new RAM but it always has errors when running a memtest. I tried every slot on my CPU but it failed. I don't know what is the issue as everything is new. Can someone please help me?
