The maximum temperature for your Pentium D 805 processor must be 64.1°C, if the current temperature is between 70°C and 90°C this means that your processor is overheating, also the black spots on the processor are sign of overheating. Remember that this dark spots are consider physical damage and eventually will damage the processor and desktop board permanently.
In order to solve the overheating problem I recommend, to update the system BIOS, also try to reseat the processor and the fan; also check if your processor is properly detected by your desktop board. For more Troubleshooting information you can check the following URL:
If after performing the previous suggestions check the processor temperature again, if the the problem continues, try the processor on a different desktop board or try another compatible processor on desktop board.