proftpd not working?

To check if proftpd is running

ps -ef | grep proftpd
proftpd  15530     1  0 21:26 ?        00:00:00 proftpd: (accepting connections)
iain     15731 13855  0 21:49 pts/1    00:00:00 grep proftpd

To find out what is bound to port 21

sudo lsof -i :21
COMMAND   PID    USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
proftpd 15530 proftpd    1u  IPv6 1641458      0t0  TCP *:ftp (LISTEN)

The output you get from the above should help you narrow things down a bit.

Edit

The problem you are seeing is likely because you are starting it in standalone mode but inetd is still configured to manage the service. You need to disable this inetd behaviour . Have a look at this page on the proftpd website - point 3 is relevant.