why linux can't see my memory

[Long Wind <longwind2009@gmail.com>]

the install CD says during installation:
not enough memory to load specified image

According to memtest I have only 688k memory at first
I really have 1 G memory
In memtest I select configuration, Memory Sizing,
and use probe method, memtest find 1 G memory

I have plug a disk that have wheezy, but can't boot it
probably  because linux can't see 1 G memory
I believe I need to change grub/kernel option to solve the problem
but I have not have any success
Can you help me?