Ram gone bad...I guess......how does that happen?

I've been using Corsair value select ram 1333Mhz(1 stick-4GB) and today i saw that Windows would not boot so i reseated the ram and it did but before loading windows it blue screened and then when it restarted it got stuck at the Mobo loading screen thingy. Somehow i managed to get it to reboot but when i was within Windows applications began to take extremely long to start up and would hang but this would never happen before. Suspecting that something was wrong i thought it was a virus and re-installed windows to be sure. However, same result. Then i thought it could be my hard disk so i used the windows disk check and it found no bad sectors and needed no repairs. Then i ran memtest which ran for 2hours without any errors. I do feel that it is the ram as applications take long to start up and things become laggy and when i listen to music it the song skips in between. I tried playing a game, the loading times increased and it too was getting stuck very slightly. I tried Nfs hot pursuit and while playing the game i noticed graphic corruption,like the road ahead would turn into water of fully black. Getting scared that it was my graphics card i used OCCT and kombuster to be sure but everything ran fine and error free. Does bad ram lead to texture corruption? I had it overclocked to 1600Mhz and sometimes even 1640mhz at 1.65v for around a year. Thought that these volts were safe as i had heard that 1.75v is the max for DDR3 Ram. Is my ram screwed? What could have lead to this?

I only have 1 stick of ram. Okay i just tried watching a movie and it was getting stuck. I will try it again using the onboard graphics. Happening with onboard graphics also. Could it be my hard disk?
Edited by jason387 - 10/18/12 at 9:24am

In my first post i did mention that i did test the hard disk but it came out clear and error free. Even defragmented the dives to make sure. Did everything possible. Had my hard disk for a year now. It's the 500GB Seagate Barracuda 7200Rpm. It's been a year now will it still be under warranty? What are the other symptoms of a bad hard disk? Could it be my mobo or processor by any chance?

I don't have a spare and since I'm using the cooler master extreme power supply 460Watts which should be enough since i have a dual core and a 6770. After overclocking all components and checking my max power consumption on load it wasn't more than 340Watts.
Please help guys really confused with this. I have nortorn anti virus and a pop up came saying high disk usage when the computer was on idle. Just happened.

I just re-installed windows so that can't be it but as i open up a folder the hard disk usage goes extremely high.