IPKVM (or similar) to the slave server(s) to see what is going on. Check logs, services running, network, processes, server load, etc.
If you cannot connect still, contact your data center/server provider and ask them to assist you in a connection (SSH or server control panel), and quick analysis.
One (or more) of your log files will probably tell you what the problem is -
/var/log/*
Obviously, make sure you are not starving the server and have enough resources for it to operate properly.