I have a client who used hostgator's online web builder "sitebuilder" which I can log into to remove the old site.
I've built a new site and now need to upload it.
The problem, I can not log into hostgator's cpanel with my computer, using the client's ID and password the client can log in. But it's like I'm locked out.
I have the firewall turned off.
Any ideas?
thanks

I'd say have your client contact Hostgators over-friendly support and have them take a look at the problem. You can always log into their chat and see if they can assist you since you have the FTP details. Did the client give you his root FTP info or did he create an FTP user for you? That may be the problem.

Can your client login from any computer? Home or work?