WHM not loading - changed main server ip address ?

Not sure where you look to fix this as I never came across this before. Client grabbed 2x 15 day trial WHM licenses which will be later updated to paid ones.

• Ubuntu old server = non-whm based ip address = ipold
• RHEL 6.2 new server = whm based ip address = ipnew

1. installed trial WHM license on new server at ip address = ipnew all setup and working fine
2. now client wants to keep the old ip address, so he powered down both machines and switched the ip addresses so that new server whm based has the old server ip address = ipold and registered a 2nd trial WHM license with ipold ip address

Problem
problem is now the new server won't load WHM on port 2086/2087 for only me i.e. ipold:2086/2087 won't work for me, but works for my client ?

1. when i access ipold:2086/2087
   i get could not connect
2. when i access ip address direct at ipold i get redirected to
   ipold/cgi-sys/defaultwebpage.cgi
3. when i ping ipold from my pc or my other web servers i get timed out responses
4. but when i ping from ipold server or ipnew server it's fine
5. I stopped csf and iptables isn't running
6. but i can access ipold server via ssh2 telnet

-----
I got the client who has access to WHM on ipold/whm to change main shared ip and site ip to the old ip address and verified the following locations have the updated ipold ip address on the RHEL 6.2 server:

• /etc/sysconfig/network
• /var/cpanel/users/username
• /var/cpanel/userdata/username/domainname.net
• /var/named/domainname.net.db
• /usr/local/apache/httpd/conf/httpd.conf

So what am I missing that isn't allowing me to load WHM but allows my client to ?

 

Thanks Tristan did try clearing DNS cache method didn't work, but ended up just adding a 2nd ip for a 2nd change of WHM main ip to this ip address as shared ip and using old ip as dedicated. Then fixed everything up and can get access back to WHM via the 2nd ip added.