Sounds like you have bad ram, bad psu or a bad hard drive.
Use Memtest86+ to check your ram one stick at a time. I usually run the test for ten minutes, if any errors show up RMA the ram...most ram is lifetime warranty today.
To check the hard drive go to the hard drive manufactures site and get their diagnostic software, make a bootable disk using the ISO file and check the drive. Use the 90 second test first, if it tells you the drive needs the long test, run it. In the end it will tell you if the drive is bad or not.
The only way to see if it is the psu is switch it out with a known good psu....borrow a friends/relatives if need be.