secure channel between clients and server has broken

hi,i have a network with 1200 clients and 3 servers that act as a domain controller,primary secondary and so on,
computer names disappear from active directory and i have to rejoin all these computer to the domain,although i have enabled active directory recycle bin but no computer name was found in deleted ou, i should mentioned that i have lots of net logon error in event viewer,my server are win server 2008 r2 and clients win7 and xp and servers run on virtualization method EXI5