Squid Proxy process not running

Squid Proxy process not running

Hey community,
some days ago my squid crashed. I'm running squid 2.6 STABLE21 on CentOS.
The output of the "show squid status" command is just
squid dead but pid file exists
starting the service displayed an "OK" but trying to stop the squid
failed. The weird thing is, that the squid service is not listed in the
"Task-Manager"
So I deleted the /var/run/squid.pid file and tried to restart the service,
but I got the following message after executing the command:
squid: ERROR: Could not send signal 0 to process 3618: (3) No such process
Even restarting the system after that changed nothing.
Also I found some interesting stuff in the /var/log/squid/cache.log
2013/08/20 07:57:43| /var/spool/squid/swap.state: (30) Read-only file
system FATAL: storeAufsDirOpenSwapLog: Failed to open swap log. Squid
Cache (Version 2.6.STABLE21): Terminated abnormally
I didn't change anything recently. Why is that a Read-only file system now?
I really hope these error messages make sense to someone of you. Any help
will be highly appreciated!
Rob