32 bit VM supported only 3GB Physical memory

Issue: Our Oracle Applications (ebiz 12.1.2) were on physical servers. We were migrating from physical to virtual servers. The plan was to replicate the virtual and physical servers and mount the same storage filers on both physical and virtual boxes. During cutover, we will shutdown physical server and bring up virtual server with the same IP and hostname as the physical server. This way we dont have to run conc clean and run autoconfig. So from a DBA point of view, the job was just to bring down the physical boxes; notify the unix sysadmins and they would change the hostname and IP.  This worked as expected except that after a few minutes after starting the services on the new boxes, the box would hang and you cannot even login. Reboot was the only option. We tried this a few times and it was the same everytime.
This box had 16G memory. We found that only 3G was being allocated as seen from /proc/meminfo.

Solution:To remedy this, we had to install a new kernel " 2.6.18-164.15.1.0.1.el5PAE" which supports memory sized greater then 3GB.  After upgrading the kernel the system now shows 16GB, and does not hang anymore.