Mac Pro does not recognize RAM

just installed 2 memory sticks of 4 gb each on mac pro (initially 6 gb ram). new sticks recognized fine slots 3&4 (where old 1 gb sticks were) displayed empty - total of 12 gb of ram vs intended 14.
restarted computer, hoping solve problem, , slots 2, 3 & 4 show empty 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

sticks had used upgrade are:
4gb ddr3-1066 (pc3-8500) 512x72 cl7 1.5v 240 pin ecc dimm

running snow leopard 10.6.7.

appreciated...

 

for memory weirdness recommend zapping pram , smc reset.

re-read instructions on order , slots apple.

finish seating 1 of old sticks screwing else , mad @ myself wasting half of day.....

 

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