1- Don't use AMD overdriver to OC.
2- Always OC from the BIOS.
3- The 635 is a locked CPU that means that u can't change the multiplier CPU to rise or drop the speed of it in that case u need OC with the FSB (bus speed as u call it) but rising the FSB u also change the RAM speed because both are linked. The 1st thing that u need to do is slow down the RAM speed to 667 after that u can start to rise the FSB.
Don't forget test the stability of the rig with prim95 3 hours, OCCT 2 hours or LinX 1 hour because that u can boot or log in doesn't mean that the rig is stable.