Go to this site: http://www.dell.com/support/drivers/us/en/19/Product/inspiron-1545 and download the driver under BIOS. Make sure all apps are closed and your PC is plugged in before flashing and follow the directions carefully or you can ruin your computer. After this, download realtemp: http://www.techpowerup.com/realtemp/ and run the exe after extracting the file. Tell me your temperatures for each core. good luck

 

You should install fresh copy of the operating system and drivers both may be it will solve your problem. And if the same problem persist again then give it to the service center for hardware check up.