optiplex 780 ddr3 issue

hi everyone,

i've just bought some extra ram for my dell optiplex 780 (DT), which is Dual Channel DDR3 Corsair Value Select, 2 x 2 Go, PC3-10600, CAS 9

once inserted, (tried with swapping modules - just one and swapping banks) no way to boot, just an awful sound from the buzzer ^^

question : are this ram modules compatible with this computer ?

btw, i found out that 'it should be' according to the kingston site (on which you select your computer and it tells you what modules are for you ^^)

thanks !

claude