I know that you're supposed to use the same CC for your reservation at check in. But my bank did a mandatory switch to chip cards so I got a new card with a new number/expiration, ect.

Is this going to pose a problem?
Should I bring the original card as well, even though it's invald?

I called my hotel and told them I lost my card and had to get it replaced.  I was able to put the new card number on my reservation with out any trouble.

I would call the hotel you are staying at as soon as you can to get the number replaced.

My hotel is going to put a hold on my card on teh 2nd even though I am not arriving until the 3rd.

Good luck.  

You may want to also let your CC company know you are travelling so they don't flag it as possible issue.