Mac Pro won't startup blinking power light

[albehany]

Howdy folk,

got the delivery of new 16GB of Ram apple ram
http://store.apple.com/us/memorymodel/ME_MACPRO_S10_RAM
this week, and have finally got the time to pop the side of my 8-core and try to install.
Processor 2 x 2.4 GHz Quad-Core Intel Xeon
MAC PRO Mid 2010
i add the 16gig to the default 6 gig i should have 22 gig
However! When I do, and re-power the mac all I get is a flashing power light (pretty sure that means a RAM issue).
Note:
if i remove the 2X8 gig mac pro work
and if i remove the old 1X6 gig ram Mac Pro work
but if i but thin toghter lashing power light and no work
I was under the impression I could run different sized and speed modules of ram

 

[Macsonic]

This also happened to me before. Found out one of the ram sticks was defective that causes the blinking start up light. Upon replacing the defective ram with a new one, the Mac Pro worked fine.

 

[DanielCoffey]

How have you got the ram arranged in the slots? Tell us what About This Mac - More Info - Memory shows you.