on a working computer ( or operating system on the same box)
go to the redhat site and use YOUR paid for tech support
the license gets you not just the SECURITY updates but support also RHEL is not free
http://www.redhat.com/support/
if you never intend to PAY for rhel5 then do not use it
install CentOS 5.5 -- it is the community supported version
you might need the ndiswrapper to use microsoft dll's that is on the RHN
also there will be an error in the system logs
the logs are located in /var/log
the boot.log , massages , NetworkManager
to read most of the logs you will need to be logged in ( in the terminal) as root
posting the error would help