It's safe to open up your computer and stop the fan with your finger (okay, relatively safe so you don't sue me).
If it's your CPU fan then either replace it with stock or consider getting a new Heatsink Fan combo.
I always get a large heatsink with 120mm fan. Read reviews and make sure it fits. Many large heatsinks don't even need fans as long as you have proper air flow (bottom front 120mm fan and top rear 120mm fan are best).