TOAD not starting or not able to connect to Oracle

​While using TOAD sometimes TOAD doesn't start due to some dll file missing(I don't remember its name currently).
But if you check that dll file will be there at the same place but some character appended to its name causing that issue.
You just need to change its name to what TOAD is searching & TOAD starts.

Now sometime TOAD is not able to connect to the Oracle instance but SQL Plus can connect.
So check listener.ora, tnsnames.ora & sqlnet.ora file for the following in order -
a) check if SID & service name is correct to which TOAD is trying to connect, like for me it is orcl
b) Restart the oracle services from services.msc in Windows, if you made any change in any of the above files.
c) If still TOAD is giving some ora-***** error, then go to next.
d) See if (PROGRAM = extproc) is present in listener.ora file, if yes then remove this statement.
e) Do step (b) above, if no success then try next step.
f) Make SQLNET.AUTHENTICATION_SERVICES= (NONE) in sqlnet.ora.
g) It should start now or may be giving error that 'C:\Program Files (x86)\Quest Software\Toad for Oracle' is not writable.
h) Change the properties of the folder by unchecking the 'Read Only' option.

Now try.