PC hardware forum: Memory problem?

I just built a new pc
Intel i3 dual
MSI Geforce gts 450
4gb (2gb x2) Super talent memory
500gb Seagate barracuda hdd
Gigabyte p55-usb3 mobo
750w PSU

I was having TONS of problems installing windows xp, vista, 7, AND ubuntu. None of them would install and every one said it had a problem copying files basically. I knew my cd's weren't bad so I figured it was my new 24x liteon sata dvd-rw but I replaced it with an old sony drive with no luck. Someone told me to try it with only 1 stick of memory so I did...and it worked. I tried reinstalling the 2nd stick after I got windows 7 installed and after the OS loaded I was getting tons of errors and if I clicked on pretty much anything it would freeze up and give me tons of errors unless I took that 2nd stick out.

As stated previously, the memory is ddr3 Super Talent ram, 2 sticks of 2gb on my gigabyte p55-usb3 mobo. I ran window's memory diagnostics tool and it said my memory has no problems.
Does this mean it is the mobo? What should I do to figure out where the problem is coming from and what piece of hardware I need to return?

Thank you!