Debian etch and memory issues with a PE 2950

[Pau Montero Parés]

Hello!

I have a PE2950 working with a Debian Etch with kernel 2.6.18-6-686.  
The server has 4GB RAM but kernel only reports this:

# dmesg | grep kernel
Memory: 3371012k/3407520k available (1541k kernel code, 35256k  
reserved, 580k data, 196k init, 2490016k highmem)
Freeing unused kernel memory: 196k freed

I tried to bypass the RAM detection using the grub parameter  
"mem=4000M" without luck.

Several days ago and before doing a security kernel update, the  
servers said that:

# dmesg | grep -n kernel
11:Use a PAE enabled kernel.
80:Memory: 3364876k/4194304k available (1541k kernel code, 41388k
reserved, 576k data, 196k init, 2490016k highmem)
428:Freeing unused kernel memory: 196k freed
641:BUG: warning at kernel/cpu.c:51/unlock_cpu_hotplug()
646:BUG: warning at kernel/cpu.c:51/unlock_cpu_hotplug()

Any ideas about how can I solve this problem and use the whole RAM?  
Thanks a lot.

-- 
Pau Montero Parés