It sounds like the heater isn't heating.
I had a similar problem in a Hoover Tumble Dryer and it was one of the 2 thermostats on the heater circuit.
If it is an old machine then it is likely that it is a bit rusty and may just need a flick to reset again.
These are located at the front of the machine (attached to the heater coil) and also at the rear of the machine attached to a cable that goes to the heater.
Replacing them is fairly simple once they are located.
Robert welsh, May 2008