2 potential ideas to check out. MAke sure that the belt is tight enough to
run the water pump. if everything else is working off the belt this is
unlikely, but it is worth checking out. The other thing to check is that
the electrical connections to the fan behind the rad is OK. YOu may have
accidently knocked loose a connection while changing the belt.

Hopefully one of these suggestions will help you out.

Does that engine only have one belt?
Have you checked inside the radiator, coolant level ok?
Does the fan turn On when AC is On?

   Try changing the thermostat.  Does the top or bottom hose
(depending on thermostat location in top or bottom hose, get hot while
other hose stay relatively cool.  With open radiator cap(don't open
hot), open cap before warmup and start engine and let idle.  This only
works if you can see coolant surface. When thermostat opens as car
warms up you will see sudden movement in coolant and other radiator
hose will get hot.
    Thermostats sometimes break.