Problem with Courier POP3/IMAP server (restarting)

[SuncuT]

Hello, yesterday I have started to have so problems.
My Courier POP3 server and IMAP server started to shutting down ( restarting ) after every few minutes. I mean for example some minutes everything working fine, then POP3/IMAP servers shutting down and I can't check emails. Then after 3-5 minute servers starting automatically and everything ok for few minutes and so on..... Yesterday tried to do everything but without result. What can it be and where to dig?
First is turning off IMAP server
Then IMAP server with SSL/TLS support
Then POP3 server
Then POP3 with SSL/TLS support

after ~3-5min.
all servers automatically starting

if POP3/IMAP servers is down I still can send emails to everybody

P.S I didn't did anything, so I don't know what happened

Regards