I'm assuming your drivers are updated then and you tested without the headset connected. Sometimes HD audio/modem devices are not recognized even after installation of proper drivers. This is an old solution, but it might work depending on your driver...
This should always be possible, but there may be manufacturer settings to prevent such tampering. I would be very careful as well because you could end up frying your motherboard and everything else even with the proper current. If your battery connections are not working properly you could get...
The port probably has a short if it works fine without anything connected. Take it in for servicing where you bought it. Otherwise try restoring the device to the defaults.
This looks like a battery issue, I've heard a lot about Dell battery problems when the laptop stays plugged in after it's fully charged. You may have loose connections or some burned out.
If you haven't deleted the admin user (first account) then you should still have admin rights. Go into the settings and check permissions or if something was disabled.
I'd go with BitDefender or Avast, they can find things that others can't. And tell your friend to set up additional protection as well to prevent infections in the future. A VPN is a good shield in addition to antivirus.