when i start my pc after the welcome screen i get a message that
windows logon UI has been disabled. and when i play a cd/dvd in the dvd rom after some time the pc stops and it has to be restarted.
Check for rootkit's and or viruses!
use
Sysinternals - htpp://www.sysinternals.com autoruns.exe
to see what applications and dll's load at startup
use an anti-virus, anti-rootkit and anti-spyware to clean your pc, but in my opinion if U have the time reinstall windows.
Some free anti-virus apps: https://www.avast.com https://free.avg.com
search google for anti rootkit (Sophos has a nice free app) and anti-spyware