My computer was left on when I left to Atlantic City from January 31st-Feb 1st (the hack occurred Feb 1st sometime in the very early morning)
External hack possible. I'd assume they are still monitoring and have access to your computer.
.... there's absolutely no trace of this hacker person doing anything on my computer
Not an accident.
So the Bitstamp hack people on this site think it happened on my desktop computer
Yup. Bitstamp is one of the most strictly regulated exchanges.
how in the happy fuck did it happen.....
It could have been anything from a targeted attack (somebody overheard you talking about your BTC) or a phishing attack (bad website/program). As others have stated, DO NOT ACCESS ANY BANK ACCOUNT INFO. I'd get onto a different computer and access your accounts to change all of your passwords to P@559hra53sesTh47ar3HARDt0kN0^^ (not my password).
I agree with Iranus. You'll need to completely reload your computer. I'd even 0 out the HD. Assume the person is monitoring everything from your computer. If there is any chance of tracking down this SOB, take your computer to as really good computer professional to copy your PC into a virtual box. This way the person will still think they have access to your computer, but won't. You can then have a monitor traffic monitor for this box.
If you give it to the right person and take the due care, you may be able to get the person back into your computer. Do not type anything about (emails, posts, etc.) about doing this. It can take a while, but the person will come back. Then, you'll be prepared. I think the person knew you were in Atlantic City. Think about emails, reservations, chats, documents that would have laid out your itinerary.
IMO, you have three choices:
1. Try to put it in a virtual machine / reverse hack (get coins back?)
2. Clear your computer completely and reset all passwords (no chance of reverse hack)
3. Do nothing, but know you are likely vulnerable.
If you go with option 3, don't access sensitive information from you computer unless you want to take the risk.
Season 1, Episode 5 of "The White Rabbit Project" on Netflix goes into detail about how they are able to pull this off. It's not just you. This is happening to banks, as well.