Re: finding computer history
Yes and no.
In the case of the notepad document that was left opened, it is almost impossible to tell if someone read it. If they altered it or something, you can tell, because you can read it and see if anything has changed. You can also right click and go to properties, to see the last time it was modified/saved, if it happened when you was away, it means someone made some change and saved it.
If someone used your Firefox browser, but it is on private or something, then this shouldn't create any logs for you to find, so again, difficult to tell if anyone has been browsing on your system (I don't used Firefox, this assumes private browsing version means it creates no internet history logs, etc.).
For your e-mails, just look in your sent file or deleted files, see if anything was deleted or sent. If you received e-mails whilst you was away but didn't look at them, they should be unread, are they still unread? If not, someone had a read of them.
You can take a look in your start menu, to look at programs listed there. However, if you already had programs listed there when you went away, it probably wouldn't help you much (unless a strange program is listed there that you never use).
In your start menu, there might be something there for "Recent Items". This will show you recently opened items.
If it is not there, open your start menu, right click on it, and click properties. In the Start Menu tab, click Customize, find the "Recent Items" check box, click it, then click ok on both windows. "Recent Items" should now be on your start menu, if it was keeping a log, it should show you recently opened items.
This will only work if the open to store recently opened items was on.