My PC is too hot.

Hi, my PC seems to run too hot:
Board temp: 52 C
CPU Temp: 67 C
Power Temp: 77 C

Its built into a mini tower (16″ x 8″ x 16.5″)
with a 300W PSU at back and a System Fan at front (no Speed control).
The system is stable and have had no boot up problems or random reboots or other stability problems. I would like it to be cooler.

Any ideas?