Loosen and re-tighten the quick releases and check both wheels to make sure they are seated properly in their respective dropouts. Do this with the bike on the ground, not on a rack or repair stand, so that the bike's weight is on the wheels. If you took off the wheel(s) to transport the bike, then re-installed the wheel incorrectly, that would effect the steering. Also, if your front wheel is not dished exactly right and you installed the front wheel backwards, it could make the bike handle differently than you are use to.