Avast is your antivirus program.
No, the 4gB of RAM isn't causing this.
More info on the 4gB Physical Memory (RAM) limit situation here: The 4gB Memory Limit
Windows will only recognize the 4gB - even if you have much more installed.
It's the issues with the STOP 0x124 error that are your problem now - and that's either a hardware problem or a compatibility problem. Have a look at this post for suggested solutions for the STOP 0x124 error: http://www.sevenforums.com/crash-loc...-what-try.html