os x server huge problem need help

Community- I owe ya big time if we can get this fixed ASAP!

For my company we have (3) Mac book Pro's and (1) iMac all connected via wifi to an airport extreme. All machines are running Yosemite 10.10.2 and the airport's software is up to date. Airport is connected to SMC Networks 1.01 modem.

I setup os x server 4.0.3 on the main iMac to allow file sharing and screen sharing both locally and through VPN. The server has been setup using the host name .private and the IP address of the iMac. VPN set up took a minute but was accomplished by opening the ports on the airport and changing it from Bridge to DHCP and Nat. I also manually added the MAC Address and Ip addresses for each device on the network. The range is good from .1-.200 and the VPN starts at .224.

Everything seemed to work fine after getting the setup correct and tested from one device. File sharing was good and seamless. However, within an hour the iMac began to get slow, started to locking folders and removing them completely. From there it completely wiped out the main user account on the iMac and has no history of any stored folders or files. As of now this am, the iMac restarts with factory settings and "sets up Mac" and the devices can still connect but cannot see any of the shared files.

I am thinking there is a permissions problem somewhere OR a Network issue with the Airport settings or Modem settings? Really to think the shared folders are gone from the iMac and no longer accessible from the devices is extremely confusing. Especially with the iMac crash?

Any suggestions PLEASE let me know... Thanks