72C is quiet hot for 955. AMD bins its cpus for lower temps and TDP and although that actual temperature may not affect the cpu, the temp diode or other failsafes may trigger shutdowns. ideally it should be lower than 60C under load.
first try blowing off any dust from heat sinks using either a set of powerful human lungs
or can of compressed air. if temps improve, you are set.
else, if this is an old system, you will benefit from re applying thermal compound. Clean off the old compound using isopropyl alcohol, or nail polish remover diluted to 90% with water. dab a piece of cloth in that solution and then clean off the compound.
reapply new compound, arctic silver 5 and then install the heatsink on the processor.