alienware X51 keeps beeping when power on, cannot get into windows nor bios

the model of my alienware x51 is R1

i7 processor, gpu gtx 555 

i changed a new hdd and added a ssd as OS disk and upgraded to 16gb ram

it was ok that i could use it normally after i upgraded

however, in the system info, it showed 16gb ram, but only 8gb can be in use

i then tried to update the bios from A03 - 06- 07 finally to A14 see if it will help

after A14 was successfully updated, i turn on the computer and it said no bootable disk found

then i restart it again and problem came!!

keep beeping with 2 short sounds

i unplugged all ram, hdd, ssd and gpu and replugged, but still not ok

what can i do to solve it?

many thanks for your help!!