Is this a computer you are using at work ?
one you got used from a gov. office and are using at home
i ask because RHEL 5.6 is a bit old , and red hat is not a free operating system
You need to have a paid license and register it with red hat
RHEL5.8 is the current in the old 5 series
If this computer has not been upgraded to 5.8( form 5.6) then it has not received any SECURITY
updates in over a year.
( With the exception of back porting them to the old 5.6 - and that is not cheep )
if this is a box you are using in a govt. office your tech support / your system admin will have the needed info
if not ?????
you might not be able to install any needed software needed to fix this .
Some information on the hardware will help
"sis3.sh" is a good start if you have no idea what is in the computer
it is an interactive shell script for normal basic linux commands
You will need to be root to run it
using two monitors normally needs a 3d card ( and the driver )
option "5" in the script lists the PCI devices
one of them is the video
or use the terminal
lspci | grep VGA
and that will output the graphics card/ chip if there is one