Morning neoyoyo,
ok, here’s the deal on SYSDBA versus NORMAL users.
If I connect as SYSTEM as SYSDBA, I will NOT be connecting as SYSTEM, I will in fact be connecting as SYS - as I showed you in my first reply. If I connect as your user AS SYSDBA I will not be connecting to your user, but to SYS.
This is why it appears that you can login to your user AS SYSDBA, but you are not, you are connecting as SYS instead.
So, that’s a red herring I’m afraid.
Oh, your images are not coming through to me by the way, I use my email system and I get your text, but not the images. I’m having to logon to the web site to see them 
The fact that when you tried to login as your user, as normal, with the changed password, and still got the invalid username/password error is interesting. This means that the problem isn’t with Toad, but with Oracle. Hmmm.
Equally, attempting to connect with a database name attached (ORCL I believe) is failing too. However, you appear to be using “ezconnect” format strings. Try just using the database name after the ‘@’ - in your case, it looks to be orcl. So:
connect IMEICOMCEL/passwordx@orcl
If this doesn’t work - and it should because you have a listener.ora set up correctly, from what I can see, then I will need to see the following:
tnsping orcl - send me the output from that command. It will show if you are reaching the listener.
sqlnet.ora if you have one. It’s in the same place as listener.ora and tnsnames.ora. It’s not a problem if you don’t have one. At least, not yet!
tnanames.ora if you don’t have one, this is your problem. You will need one. It tells Oracle how to get from “@orcl” to localhost:1521/orcl.
It will look something like the following:
orcl.world,orcl =
(description =
(address_list =
(address = (protocol = tcp)(host = localhost)(port = 1521))
)
(connect_data = (service_name = orcl))
)
This is off the top of my head, and is for an 11g database. I’m not up to 12c yet, so bear in mind that there may well be differences.
My own test (11g) database is called ant12. It accepts me connecting as follows:
connect nod/nod
connect nod/nod@ant12
connect nod/nod@localhost:1521/ant12
And I do not have a sqlnet.ora. I do have a listener.ora set up similar to your one, and a tnsnames.ora set up as shown above, or very similar to it.
However, if you use the “ezconnect” connection string format, as shown in one of your example, then you should not need the tnsnames.ora file, as you are already supplying the details on the connection string. Very strange.
One final thought, do you have a firewall on this computer? It could be that Windows 7’s firewall is preventing you from getting through the network. Even though the database and client (toad, sqlplus) are on the same computer, using the TCP protocol is going to hit the network.
You could try this in a Dos session:
set %ORACLE_SID%=orcl
sqlplus MEICOMCEL/passwordx
If that works, then your problem is almost certainly the firewall.
HTH
Cheers,
Norm. [TeamT]