Zen Hangs up

Hi Guys, over the past two weeks I've been having an issue where zen basically crashes, the only fix I have had is to reboot the server a few times per day... It's 10.3.4 on server 2008r2 with a MS sql server hosted on another server. By crashes I mean I can not get to the web interface to manage anything, and users are getting an error that the password or certificate are incorrect. I've checked the basics, plenty of free space and all the SQL maintenance is running nightly. Where can I look for a crash log or anything that may help out?

Thanks!!
Dennis