And since you are not using a support service I'll offer a test I use to sniff out if this is hardware or software.

But first, since this machine had DSL it's possible you had some DSL MODEM driver installed. I don't see where you removed that. Sorry I can not tell you how to. I've seen dozens of such PPPoE DSL software over the decades so I can't guess which method to use.

With that out of the way, I'm also hampered by the lack of a quoted "error message."

Moving onto the test I use. I boot a LiveCD called Ubuntu and see if I can get on the internet. No install needed, no learning Linux either.

More at ubuntu but for 99.99% of the time I boot the LiveCD and then pull up FireFox and I'm in. If there is hardware or windows software issues you have to tackle that.

In parting I've lost count of posts like yours when the antivirus expires.