sounds like your coolant fan isn't kicking in when it should
first, check to see that the coolant temp sensor is still plugged in
then
turn the coolant fan with your fingers (with the car switched off)
the fan blades should "glide" round with ease.
(if it doesn't, the fan's broke)
then if you still can't find it...
check to see you havn't just blew a fuse
then, if no fuses are blew...
let the car warm up, let it get hot, but not so it touches the red marker
in this time, the fan should kick in to cool the engine down. if it doesn't you should take the coolant temp sensor out, and test it.
if the fan is comming on, you might just have a air leak...or not anuff water in