Dell T7500 will not start after memory upgrade

Is the new memory registered or unbuffered? My guess at this point is that you are mixing the two types (there is both registered and unbuffered ECC memory). I can't find any info on the Centon so its a bit hard to troubleshoot.

The original memory I have is unbuffered (ECC).
The new memory I got is ECC (not registered), according to the order I placed and the delivery info.
But I can't confirm this by the code that's actually on the memory stick. I also couldn't find this code anywhere on the web or on the Centon web site, as you have experienced.
What's surprising is that when I take those new sticks out and use only my original memory, the computer still will not boot (it wasn't starting at all, but it does now, after taking some memory out).
According to the Dell diagnostic lights (in the manual), this is caused by bad memory. But I tried first with only two sticks in (one in the motherboard, one in the riser, each at slot 1), then replaced these two sticks with two of the others. The computer is only two months old, so all the sticks can't be bad. Then I went to 4 GB (two in the MOBO, two on the riser, each at slot 1 and 2). Still no boot.
Usually when I start this machine, the fans go on for about 15 seconds and then it becomes very quiet, but now the fans are running non-stop. And nothing on the monitor.

Did you resolve this problem? I have the exact same problem with my T7500 and cannot resolve it!  

Yes, that's what solved the problem for me.
I had a Dell tech come over (I have a maintenance plan), and afterwards brought it to a shop and both couldn't solve the problem.
It's by watching what they did and didn't do that I found the solution.
The shop almost had it but put the memory sticks back in the wrong order.

Dell really should know about this. Their tech had no clue.
Congratulations for finding on your own!

For anyone else who has this problem here is the link to the manual's page to remove the heat sink and dual processor:
http://support.ap.dell.com/support/edocs/systems/wsT750...

I was pretty close to sending the machine back to Dell as it appeared pretty much like a terminal failure. I'm glad I persevered, even if I did lose almost a whole day.

Yes.

Just follow the manual's instructions in the link I posted.
Take everything apart and put it back together.
Unseating the card and re-seating it seems to work as a reset when more memory is added.

Best answer selected by rpvs01.

This topic has been closed by Maziar