Not sure if this is your issue our not, but we have had a lot of issues with failure to be able to login to the controller at one site, only a reboot seemed to fix it for a while... After working with tech support for some time, we found that the software the IT department was using to scan the network for security issues was sending something to the controller that would "confuse it" and cause the web server to not allow us to login or not show a login screen at all. Having the IT people add an exemption not to scan the 3300's IP addresses stopped the problem from recurring.