Hmm, it’s possible that you’re running out of memory. You may want to run the command “dmesg | tail -50”, and see if you see any Out of Memory (OOM) related errors.
Also, you may want to look at the “ps auxw” list, and see if proftpd is running still.
Recommended memory for almost any control panel is min 1GB and if you think to have low to medium traffic CMS site then at least 2GB. VPS with 512MB of memory is good for testing or if you think to deal with everything manually but not to have control panel.
Other solution you could try is to turn off all services and use them externally, instead of bind use dns from you domain provider or cloudflare, instead of postfix use external email like zoho with 5 free users/emails (alternative to google apps), then if you turn off your email you dont need anymore spam and virus protection so turn off spamassassin and clamav including usermin… and so on. Then maybe you will have a little more memory to run everything.