Ubuntu – Ubuntu 14.04 (amd64) not detecting all of the memory

I've got 4gb of RAM installed in my machine but Ubuntu only detects 2.8gb of RAM

If I run uname -a I get:

Linux DeLillo 3.13.0-24-generic #46-Ubuntu SMP Thu Apr 10 19:11:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

Which seems to confirm that I'm running Ubuntu in 64-bit.

I also have an nVidia graphics card installed that may have memory allocated to it. But 1.2gb seems a bit excessive.

I've had a poke around in BIOS and can't seem to find any settings to change the amount of RAM allocated to my GPU. Is this just something I have to live with?

EDIT: sudo lshw -class memory outputs:

PCI (sysfs)  
*-firmware              
   description: BIOS
   vendor: Phoenix Technologies, LTD
   physical id: 0
   version: 6.00 PG
   date: 06/19/2008
   size: 128KiB
   capacity: 448KiB
   capabilities: isa pci pnp apm upgrade shadowing cdboot bootselect socketedrom edd int13floppy360 int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer int10video acpi usb ls120boot zipboot biosbootspecification
*-cache:0
   description: L1 cache
   physical id: 8
   slot: Internal Cache
   size: 32KiB
   capacity: 32KiB
   capabilities: synchronous internal write-back
*-cache:1
   description: L2 cache
   physical id: 9
   slot: External Cache
   size: 4MiB
   capacity: 4MiB
   capabilities: synchronous external write-back
*-memory
   description: System Memory
   physical id: 24
   slot: System board or motherboard
   size: 4GiB
 *-bank:0
      description: DIMMProject-Id-Version: lshwReport-Msgid-Bugs-To: FULL NAME <EMAIL@ADDRESS>POT-Creation-Date: 2009-10-08 14:02+0200PO-Revision-Date: 2012-02-05 00:26+0000Last-Translator: Andi Chandler <Unknown>Language-Team: English (United Kingdom) <en_GB@li.org>MIME-Version: 1.0Content-Type: text/plain; charset=UTF-8Content-Transfer-Encoding: 8bitX-Launchpad-Export-Date: 2014-04-10 12:53+0000X-Generator: Launchpad (build 16976) Synchronous 50410 MHz (0.0 ns)
      physical id: 0
      slot: A0
      size: 2GiB
      width: 64 bits
      clock: 3165MHz (0.3ns)
 *-bank:1
      description: DIMMProject-Id-Version: lshwReport-Msgid-Bugs-To: FULL NAME <EMAIL@ADDRESS>POT-Creation-Date: 2009-10-08 14:02+0200PO-Revision-Date: 2012-02-05 00:26+0000Last-Translator: Andi Chandler <Unknown>Language-Team: English (United Kingdom) <en_GB@li.org>MIME-Version: 1.0Content-Type: text/plain; charset=UTF-8Content-Transfer-Encoding: 8bitX-Launchpad-Export-Date: 2014-04-10 12:53+0000X-Generator: Launchpad (build 16976) Synchronous 50410 MHz (0.0 ns)
      physical id: 1
      slot: A1
      size: 2GiB
      width: 64 bits
      clock: 3165MHz (0.3ns)

Which suggests that it's detecting two 2gb sticks of RAM, but free outputs:

           total       used       free     shared    buffers     cached
Mem:       2822496    2575872     246624      70960      15316     338656
-/+ buffers/cache:    2221900     600596
Swap:            0          0          0

EDIT 2: just ran memtest. It correctly reports that I have two 2gb sticks installed, but claims my total memory is 2814mb. When it tests slot0 it runs from 196kbs – 2048mb and then when it tests slot1 it runs from 2048mb – 2815mb. It also claims my cached memory is 2814mb with 332kb reserved.

Everything else (FSB, memory speed, caches, etc.) seem to be reported correctly. BIOS correctly reports that I have 4096mb installed. I now suspect this is a hardware issue.