Mac Pro does not recognize RAM

[sawihsiwi]

Just installed two memory sticks of 4 GB each on my Mac Pro (initially 6 GB RAM). The new sticks were recognized fine but slots 3&4 (where old 1 GB sticks were) were displayed as empty - for a total of 12 GB of RAM vs intended 14.
Restarted the computer, hoping that will solve the problem, and now slots 2, 3 & 4 show up as empty for only 11 GB of RAM.

Hardware Overview:

Model Name: Mac Pro
Model Identifier: MacPro5,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 2.4 GHz
Number Of Processors: 2
Total Number Of Cores: 8
L2 Cache (per core): 256 KB
L3 Cache (per processor): 12 MB
Memory: 11 GB
Processor Interconnect Speed: 5.86 GT/s
Boot ROM Version: MP51.007F.B03
SMC Version (system): 1.39f11
SMC Version (processor tray): 1.39f11
Serial Number (system): H00360ZREUF
Serial Number (processor tray): J503201CKBH8A
Hardware UUID: 1EBD8D6A-075A-5D0C-B430-3766BE9566CE

The sticks that I had used for the upgrade are:
4GB DDR3-1066 (PC3-8500) 512x72 CL7 1.5v 240 Pin ECC DIMM

This is running Snow Leopard 10.6.7.

Any help will be greatly appreciated...

 

[drrbc]

For memory weirdness I always recommend zapping the PRAM and a SMC reset.

The I re-read the instructions on which order and which slots from Apple.

Then I finish seating one of the old sticks that was screwing up everything else and get mad at myself for wasting half of my day.....

 

[Joetazz]

Hi, I get that problem as well but I find it sorts itself out by powering down and unplugging (SMC?). Or try moving the RAM around that worked for me.