May be vnc server is not allowed in Firewall, if we allowed vnc in firewall we can connect with other clients. If that is also not working, we have to add Dword key in registry.

To add key in registry, open registry by regedit.exe command.

And go to HKEY_LOCAL_MACHINE > Software > Microsoft > Windows > Current Version>Policies >System and create a New DWORD 32 or 64 bit value with the following
LocalAccountTokenFilterPolicy and change the value to 1.
Now vnc can connect with Other clients.

We can use checkdisk to check and fix Operating systems error and HDD Bad sectors errors. Also can Use System recovery disk to recover the systems. If system is not booting to system repair, or safe mode, we can disconnect the hdd and connect that to other system as a slave.Now we can run the check disk to troubleshoot OS.