Your machine is compromised, so the hackers are simply stealing the post 2FA session tokens from your computer. Basically, once you enter your password and complete the 2FA challenge, the server grants an access token to your computer so you don’t need to repeat the process for every interaction with that service. If there is malware on your computer, those tokens can be stolen and reused by nefarious actors.
2FA isn’t a foolproof system; it just makes it significantly harder for hackers to log in. And they’re basically piggybacking on your successful login to hijack your accounts.
Format the machine and change *all* your passwords.
(And don’t let your little brother use your computer again)
Sounds like the drive is dead. They are mechanical devices which tend to wear out with use. Literally magnetic platters spinning at 7200rpm with heads floating on a cushion of air a few microns above the surface. Just a single speck of dust that gets in there can absolutely destroy the drive, as can moving it while it’s spinning, or it could have a manufacturing defect that causes it to prematurely fail for no other reason whatsoever.
The best you can really hope for is that the drive is still covered under warranty and get it replaced by Western Digital.