Is it where the DSL light is stable but you're not getting any IP (hence not connecting)? If so, happens to me more than a few times. The port hangs but its on the local switch. The TM CS can't detect it. Only a technician knows and can fix it.

Yep I experience this a lot

If a disconnection occurs , I can't connect at all. It would just say invalid user name/password , but after for a while it would eventually connect. I am not sure why it occurs

A technician had to come and fix it. To be exact, they have to go to the switch you're connecting with and reset your port. If they check from your house they can clearly see your port has hanged. But from TM CS, they can't see a thing. It's a really pain in the ass explaining to them after it happens so many times.
The technician said to me its the port that hangs. The port on the local switch. Not the kind of where your username hangs and TM CS can't fix it.

whois ATS  if this works please let me know, 175 is really crappy