Vista (64-bit) Ram Problem

Hello, First time posting here, i hope someone within these forums will be able to help me.

So, a couple of months ago i bought a custom computer (bought all parts then put it together myself), and i have been happy with it completly.

Specs:
Vista 64-Bit
CPU: AMD Phenom X4 9850 (2.5GHZ)
Graphics: ATI Radeon 4870 512MB
Ram: 2 GB of DDR2 PC8500
500 GB of Hard drive Space


Now nearly 2 months later, i have decided to add 2 more GB of Ram. So i ordered 2 more GB and received it today. Now at first, i have NO success with putting all 4 GB in. So i decide to try 3 for now. It gets to the windows loading bar, but it just stays loading and never goes past that screen. All attempts with 3GB after that resulted in the computer restarting just after i select "safe mode" or "start windows normally", or even "boot from last good configuration". So it doesnt even reach the Loading Screen. I have tried just the 2 new sticks by themselves, no problems. I have also tried 1 new stick and one old stick, and still no problems. I have tried all combinations of the slots for the ram, and it all works, as long as i don't have more than 2 GB of ram in at one time. In the Bios it does recognize that i have 3GB or 4GB of ram in, but it still will not boot, as it will just keep restarting before it gets to the windows load screen.

Can anyone help?

Thanks, OneBullet.