Can't Start Mysql

For some reason, mysql died last night at 4 am (best as I can tell). Now I can't start it...even if I restart the whole server. Here's what's in the log:

051006 12:26:30 mysqld started
051006 12:26:30 InnoDB: Started; log sequence number 0 43634
051006 12:26:30 [ERROR] /usr/local/mysql/bin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 13)
051006 12:26:30 [ERROR] Can't start server: can't create PID file: Permission denied

This is running as root...and there IS no mysqld.pid file in /var/run/mysqld, either, so it doesn't seem like permissions are wrong.

if I try to start from command line, I get this:
[root@server mysql]# /usr/local/mysql/bin/safe_mysqld &
[1] 3680
[root@server mysql]# Starting mysqld daemon with databases from /var/lib/mysql
STOPPING server from pid file /var/run/mysqld/mysqld.pid
051006 12:29:28 mysqld ended