If you edited your crontab file using a windows editor (via samba or something) and it's replaced the newlines with \n\r or just \r, cron won't run.
Also, if you're using /etc/cron.d/* and one of those files has a \r in it, cron will move through the files and stop when it hits a bad file. Not sure if that's the problem?
Use:
od -c /etc/cron.d/* | grep \r