Can you pitch to much yeast?

I think my fermentation stop early. I will check my gravity tomorrow on day three. I was wondering if it is not at the right gravity. Do I just pitch more yeast? Here is the back story to my question. I brewed up an Oatmeal Stout. Pitched the yeast at about 80 deg. The next morning I got up and that air lock was rockin. Then, about 16 hours later it was stone cold dead no movement. Thank you for you help
I am a newbie so I worry alot

Relax....

Your beer might have just finished up already. You won't know til you take a hydro reading. I'm not a fan of repitching unless it's been a month of no action.

I just had batch that got stuck, I agitated the bucket gently to re-suspend the yeast (just moving it out of the closet to take a grav reading and back again), then wrapped it in a blanket and left it alone for another 2 weeks, it was fine.

You really don't want to repitch unless you really have to...

What's your yeast strain? Some yeast can really do their stuff fast. Take for example, the Wyeast Ringwood Ale Yeast, it can complete a low gravity beer in just 24 hrs or less!

I've had beers ferment out in 24 hours before.

Beer doesn't just cease to ferment once it's "rockin" as you say. It either never starts (very rare) or it slows down slowly and falls short of target gravity.

You're beer is likely fermented out. Take a reading. Plan on letting it sit for aminimum of another 2 weeks (regardless of the instruction manual).

Well is it possible to still pitch too much yeast? Like say I wanted to do a 3 gallon batch. Could I still pitch a whole packet of dry yeast and it would be all right?

Yes you can pitch too much yeast. For proper beer flavour you need the yeast to undergo a growth phase before they start to ferment. In answer to your specific question: Probably. It depends on the starting gravity and ale vs lager.

GT

It is very difficult to overpitch yeast. You would need to pitch a very large starter - an extra packet would not do it. I threw together a rough guide here on yeast starters that talks about proper sizing.

Cheers,
Brad