I was accused of getting into a file at work that I didn't get it it's an online system and I was there that day but did not do it and my HR won't believe me what do I do

So ? There is no way to prove you did not do something. They are requierd to prove you did it. Can they show that you logged n to a specific computer with your password and got the information ?

Always be certain that you log off when you get up from your workstation. Hacking is easy enough without you eliminating a step for the hacker. For this instance, you need a copy of the access log for that file before you accept anything they say you did.

If they try to intimidate you, there's lots of news sources that love stories about companies getting hacked.

'There that day' isn't the basis for an accusation of this sort. Being the user of a specific computer is, or being the one logged in under YOUR name on any computer is. If you were foolish enough to forget to log out, or to let someone else use it, or even to just go to the bathroom or lunch and leave it open, then the blame is on you.

As Chuck says they have to show proof that you did. However, with modern systems, they can tell if a file was accessed by a certain ID. And that is probably the proof that they have. Now it could mean someone knows your password or you left a computer unattended while logged in to it. And there is no way to prove either case. So if they have a log that shows your ID accessed the file, that is all they need.

You have a right to ask to see the proof.