It is hard to say what can be wrong but I'd start with disabling all third-party plugins and check RubyMine's log (Help|show log in ...)
Hope this helps, Oleg.
I have a similar setup, but with Ubuntu 13.10.
The process RubyMine was attached to I had to kill it -- and used a -9 to do so.
You might also try boosting the Java Heap size.
I changed to Oracle Java and everything is OK now. Problem solved.
Open JDK and any other non-Oracle jdk are not supported.