Not one to be overly suspicious, but
Blacked out for a 4 hour period and can't remember what you did on the computer; the obvious files (internet history, etc.) not being of use
versus
Someone else was on the computer for a 4 hour period, deleted the obvious files (internet history, etc.) and OP is curious what the person did.
One of these seems more likely than the other, and historically, when similar questions have been asked on these forums, the answer usually turns out to be the latter. I'm not saying that's definitely the case in the OP, but it's a possibility. And, if she deleted the cache & internet history, something's up.