My snake died

My baby corn snake just died. He just shed last Friday, so I tried feeding him tonight. He hasn't eaten since I've had him (about 4 weeks) and tonight was the third time I tried. He didn't take the mouse, so I did as I've done before: I put him and the mouse in his little Petco box(which has airholes) and closed it up and left the whole box in his vivarium. I checked back 45 minutes later to see if he had eaten the mouse, which he hadn't, but he wasnt moving at all. I shook the box a little to see if he'd snap out of it but he didn't and I finally picked him up to discover that to the best of my knowledge, he is dead. Why on earth would this happen? Ive done this same thing before and it's been fine(well, he never took the mouse before, but he kept alive!). Could he have suffocated? That's almost what it looks like because his mouth was open. I feel horribly guilty. Maybe this snake thing isn't for me after all. Help!