Motherboard supports CPU up to 95 Watts TDP (Thermal Design Power).
AMD Phenom II X4 955 has a TDP of 125 Watts. CPU is not supported by your motherboard.https://www.asus.com/us/Motherboards/M5A78LM_LX3/HelpDesk_CPU/
The Thermal Design Power (TDP) is the average maximum power a processor can dissipate while running commercially available software. TDP is primarily used as a guideline for manufacturers of thermal solutions (heatsinks/fans, etc) which tells them how much heat their solution should dissipate.