will not shift out of first gear

i just bought the car and had to replace the intake gasket. after i fixed that i drove it for about an hour, and it hesitated slightly shifting from first to second, and then after about an hour of driving it, it i went to take off from a stoplight and it would not shift out of first gear. it goes into first and reverse fine, but no matter if i try to manually shift it or not it will not leave first gear.