Is this laptop sitting on a hard, flat surface? If its sitting on your bed or your lap, it will get poor airflow. 80% consistent CPU usage is not good. The system idle process should hover around 90%+ when nothing is running. Go to Start --> Run --> Type MSCONFIG. Go to the Startup Tab. Do you have a lot of stuff checked? These are programs running in your background and consuming system resources. Go threw this list and disable anything that does not need to run upon startup. Also, have you ran an up-to-date spyware/virus scan lately?
If all of these check out fine, invest in a laptop cooling pad like this:
Have you tried cleaning out your CPU air vents? If you are using your laptop and it will work fine for a little bit then it becomes slow, it sounds like your CPU is throttling back so it can cool down. Since the laptop cooling pad doesn't work very well, it likely your laptop might need to be cleaned.
I have the opposite problem of you, my gtx260 fails to pass 65C on 40% fan(palit gtx260 sonic)
If you dust things out, it will do wonders, if the warranty is out, go buy coffee filters and some thermal paste eg: ocz freeze,acrtic cooling mx2, tuniq tx-3. Stay away from ac5, it takes long to cure and if you put too much, it can lead to problems near your graphics card chip.
try setting your cooling fan on an Aluminum or steel cooking sheet with holes drilled or cut into it where the cooling plate fans are. slice a vent hole on one of the sides of the pan. file or sand out any burrs or sharp edges. the pan will allow better airflow room and will disperse any residual heat like a heat-sink would. Also do what everyone else says and try cleaning it out. Do not take it apart unless you know what your doing. Laptops are tricky and have lots of screws. Get a can of Dust Off compressed air and try that first. Check out a website on how to clean your laptop's heat-sinks.