Cannot Overclock my Phenom II 940

Hey guys I need help,

I have a Phenom II 940 that I have been using for over a year.Recently I tried giving overclocking a shot.But the problem is no matter how much I try,my processor just cant maintain stability over 3.2 GHZ on stock voltage.I am really not a fan of over volting but just to be sure,I had set my V-core to 1.4v and set the multiplier to 17.5x which have a clockspeed of 3.5GHZ,but still had no luck,it fails the stress tests within 10 seconds.I have been reading reviews on the net and I saw the most people were able to take their 940 to around 3.7-3.8GHZ and at under 1.4volts. Does this mean that I have a bad processor or am I doing anything wrong. And I really have no knowledge of northbridge and southbridge overclocking and also I have no idea about RAM overclocking and timing settings,so any advice on that would really be helpful.

Here are my specs:
AMD Phenom II 940
Stock Cooler
ASUS M4a-785M
HIS HD 4850 icooler iv 512MB GDDR3
A-DATA 4GB DDR2 800MHZ ram
Thermaltake TR2-500W PSU.

Thanks.