Computer restarts auitomatically?

01.My computer is restarting automatically. I have installed Fansspeed software to monitor my CPU temperature. The temperature is maitained at around 75deg Cent. I have opened and cleaned cooling fans and Heat sink. But still problem is exists. Please guide me in this regard.

02. When ever my computer starts or restarts it is tell that FAT32 file is missig and asking for disk check. But the problem exists.Please guide me whether I have to reinstall my opearting system.