Blue Screen after Installing Ram [moved from Vista/ Windows 7]

I have recently bought 2 GB Ram for my Dell Dimension E520 which already had 1GB Ram installed. After I log on and I open Mozilla Firefox and open 5 tabs which have games on them the computer crashes for 3 seconds and a bluescreen appears. The bluescreen appears for 2 seconds and the whole computer restarts. When I had 1GB Ram and did the same thing (open 5 tabs and open games on them) my computer would slightly just go slow by a bit. The Ram is identical and they have been put into slot 2 and 3. This happens very often and is very annoying. In slot 1 and 4 there are two 512MB Ram put in when I first bought it. The Ram is not one of those cheap ones. When there was 1GB Ram everything used to work perfectly and none of these errors would happen!

Computer Specifications:

Intel(R) G965 Express Chipset Family
3GB Ram
Service Pack 2
Windows Vista Home Basic
2.79 GHZ
32-BIT Operating System