Hi Maricarmen,
Please try the following -
Point 1
Have you registered your IP address in HOST file ??
if not perform the following steps
in your system-->RUN-->drivers-->etc-->host (open in notepad) --> write your IP Address and type a link
(Ex: 192.168.1.1 crmserver.naga.com )
save it then try to open it through the WEB_UI
Point 2
Hope you also have the below settings in your user profile in SU3
Parameters tab > Add Parameter ID as CRM_UI_PROFILE > Parameter Value is * > Save
Hope this will be useful
Thanks and Regards
DJ