Patric, you give some details on things like how you want buttons to respond, but no overview on what you're tracking.
You say you have 400 clients and are tracking "system problems" and "customer complaints".
What service are you providing? Are you supporting a software product? Are you the help desk for a corporation, handling all support for diverse departments?
If you're providing general hardware support, how common is the hardware platform you're supporting?
If you're supporting software, are you responsible for the entire software install on numerous PC's, or only the performance of one application?
Do "customer complaints" involve system problems, ordering problems, unsatisfactory merchandise, unsatisfactory service or support?
What do you hope to get OUT of the tracking system? Do you just need to have opened and closed dates for tickets? Do you need to have a routing system to assign them to appropriate technicians and departments? Are you hoping to mine the data for common problems to allow you to pool solutions rather than rediscover them each time a problem occurs?
You could knock a basic ticket database together in about fifteen minutes with MySQL and PHP.