I have the correct RAM, specifically for the make/model (DDR2). I used exactly the same type in my daughter's 6000 and it has been fine for a year in there.
I have also swapped back the old memory with same symptoms.
Since then I have tried blowing out the 2 memory slots, etc.
What seemed significant was that in gave me a bluescreen on shutdown/restart just before it went wrong. I had to power off from that as it was just hanging.
It has not booted since.
When I switch on, there is a start screen (DELL) with a bar going across (as something is loading?), it does not complete that bar, but screen goes black. Then after about a minute it shuts off.
When I am changing memory, I keep my bare foot on a radiator all the time. No static clicks or anything like that.
This has me puzzled, but that blue screen on the restart has me worried. Frustration is that I can't boot off another cd, etc as it doesn't get that far.
Thankyou for your patience.