First off, one does not get a virus from downloading porn. One may get a virus from a combination of malicious websites and poorly designed web browsers (not mentioning any names *cough*), but the porn itself is not the problem.
Please, don't blame the porn.
That said, you can try
House Call and see if it picks up anything. House Call is a free online virus scanning utility, so if you do have a virus and Avast! isn't picking it up, House Call might be able to help you out with that.
Based on the symptoms you've described, though, I'm not actually convinced you do have a virus. Internet goes up and down. It happens to everyone, especially with broadband connections; outages are a part of life. Sometimes stuff gets write-protected too, or flagged as in use by a current process even if it's actually not. Usually in that situation simply restarting fixes the issue. Have you since been able to delete the empty folder?
As to why Kaspersky wouldn't install, do you still have Avast! running? Anti-virus programs as a rule don't play well with each other. That could very well be the problem.
In the off chance that you do have a virus, you probably won't have to do anything anyway. Avast! updates it's definitions automatically by default, so you should have the latest updates unless you've changed that. Definitions are something of a chicken-and-egg situation, and sometimes there's a bit of a lag between a new virus getting out into the wild and the definition files of AV X being updated to include it. These delays do not generally last more than 24-48 hours, so if you've managed to pick up a virus that avoids heuristics and is not in the defs, all you really need to do is wait a day or two and it should be detected. Without knowing more about the specific threat (or indeed, if there is one) that's really all there is for you to do anyway.
EDIT- Confirmed :
Kaspersky is not friends with ZA or Avast!.