Laptop monitor say's 100 degrees at start-up

My GF laptop has been shuting down during gameplay, after the start-up it say's the shutdown was du to the temp exeeding 130 degrees celcius... and the computer is never even that hot

We tried kept the laptop closed for 2 days and today when we opened it, it said 100 degrees, that seems impossible!

Could the temperature sensor be broken, can that be fixed easely ?

Thanks